ABUNDANCE, HABITAT USE, BEHAVIOUR AND MANAGEMENT

Transcription

1 ABUNDANCE, HABITAT USE, BEHAVIOUR AND MANAGEMENT OF HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE) IN THE MACHALILLA NATIONAL PARK, ECUADOR Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel Vorgelegt von Meike Scheidat Kiel 2001

2 He is the most gamesome and light-hearted of all the whales, making more gay foam and white water than any other of them. (Herman Melville: Moby Dick)

3 CONTENTS Contents 1. GENERAL INTRODUCTION STUDY AREA GENERAL STUDY AREA ISLA DE LA PLATA METHODS MARK-RECAPTURE STRIP TRANSECTS PHOTO-IDENTIFICATION SIMULTANEOUS OBSERVATIONS HABITAT CHARACTERISTICS THEODOLITE TRACKING OF WHALES MAP PROJECTIONS, STATISTICAL ANALYSES AND SOFTWARE USED INTERVIEWS DEFINITIONS CHAPTERS ABUNDANCE AND DISTRIBUTION Introduction Results Distribution of humpback whales in the Machalilla National Park Abundance of humpback whales in the Machalilla National Park Occupancy and occurrence of humpback whales in the MNP Migration patterns of humpback whales in the MNP The influence of the 1997/1998 El Niño Southern Oscillation Discussion HABITAT USE Introduction Results Habitat use around the island Determination of core habitat Trackings Discussion REPRODUCTIVE BEHAVIOUR Introduction Results Observed reproductive behaviour Group sizes Breaching as a spatial distance holder Mother-calf pairs Song Interactions with orcas (Orcinus orca) Interaction with False Killer whales (Pseudorca crassidens) Interaction with Dolphins Discussion...66

4 CONTENTS 4.4. INTERACTION WITH WHALE-WATCHING VESSELS Introduction Results Trackings of humpbacks and whale-watching vessels Changes in speed and course Differences due to group size or composition Change of speed: a case study Discussion MANAGEMENT AND CONSERVATION OF HUMPBACK WHALES Introduction The Machalilla National Park Tourism in a coastal community of a developing country Local Whale-watching Observed and potential effects on humpbacks Development of a management concept for humpback whales Political realities Discussion GENERAL DISCUSSION AND OUTLOOK SUMMARY ZUSAMMENFASSUNG ACKNOWLEDGEMENTS REFERENCES

5 1. GENERAL INTRODUCTION 1. General introduction Humpback whales, Megaptera novaeangliae, belong to the order Mysticeti and family Balaenopteridae (rorquals). They are the only species of the genus Megaptera and, in comparison to other rorquals, have a stout body with very long pectoral flippers that may reach almost a third of the body length (hence the name Megaptera large wings). The adult animal weighs on average 30,000 kg and the length of sexually mature males is in the order of 12m, females being around 14m (e.g. Martin 1990). Humpback whales occur in all oceans of the world. They conduct the longest recorded migration of any mammal (Stone et al. 1990) from their feeding grounds in high latitudes to tropical or subtropical breeding grounds. Feeding takes place during the fairly short summers in the polar regions. Because of the reversal of seasons, the populations of the northern hemisphere are not in equatorial waters at the same time as those of the southern hemisphere. Due to their predictable occurrence in their breeding and feeding grounds humpbacks were an easy target for whaling activities and one of the earliest whale species hunted by humans. In the beginning aboriginal peoples especially in Pacific waters engaged in inshore-based whaling. In the early 19 th century humpback whales were hunted by European and Yankee whalers, especially in the North Pacific and North Atlantic. With the advent of modern whaling technology whalers were able to reach more distant waters and at the beginning of the 20 th century more than 100,000 humpbacks were taken in the southern hemisphere. Although catches fell dramatically from 14,000 per year to less than 2,000 a year around 1920, whaling activity continued for several decades (Klinowska 1991). Humpback whaling was banned in the southern hemisphere after the end of the 1962 season, and the species was listed as protected by the International Whaling Commission in The species has not been subsequently hunted except for small subsistence hunts in Greenland, the Lesser Antilles and Tonga (reviewed in Ellis 1993). The pre-whaling abundance of humpback whales of all oceans combined is estimated to have been around 200,000 animals. Due to their depleted numbers, humpbacks were listed as endangered in waters of the United States (Braham 1984) and threatened in Canada (Whitehead 1987) and are included in Appendix I of the 1973 Convention on International Trade in Endangered Species (CITES) as well as listed as vulnerable in the IUCN (1996). Nowadays world population estimates vary between 10,000 and 20,000 animals (e.g. Martin 1990). World-wide, eleven populations of humpback whales were recognised by Townsend (1935) after reviewing logbook records of whalers from the 19th century. Populations are separated by density distribution, migratory routes, song dialects and differences in coloration and morphometry. In the southern hemisphere, Mackintosh (1942, 1965) distinguished 6 stocks distributed around the Antarctic continent during the austral summer. During the winter, each stock migrates towards the equator to its own coastal or insular breeding ground in tropical or near-tropical waters. Known breeding grounds for these stocks are found off Africa (Best et al. 1998; Rosenbaum et al. 1997), Australia (Corkeron et al. 1994), the southwestern Pacific islands (Hauser et al. 2000) and South America (Flórez-González 1991; Scheidat et al. 2000). Although humpbacks have been studied 1

6 1. GENERAL INTRODUCTION intensively at some breeding grounds, such as the Hawaiian islands (e.g. Herman and Antinoja 1977), hardly any studies have taken place in South American waters and current information on the population size, habitat use and behaviour is therefore very limited. Also, there is virtually no knowledge on the stock structure in the tropical East Pacific, making it impossible to determine whether these humpbacks are recovering from their decline caused by whaling. Off the Ecuadorian mainland humpback whales are found in the marine area of the Machalilla National Park from June to September. Over recent years a small whale-watching industry has developed in the fishing village of Pto. Lopez. Although the humpback whales spend the height of the breeding season in this area, re-sightings of identified individuals in Colombia have raised doubts if they really form a separate breeding population. Flórez-González et al. (1998) suggested that the humpback whales seen off the Ecuadorian coast may only move past the area while migrating to Colombia or possibly use the whole eastern tropical Pacific as a wintering ground, rather than being confined to a specific breeding site in Ecuador. In the Machalilla National Park humpbacks are frequently found around an island, the Isla de la Plata, situated about 30km off the mainland. The area around the island and especially the humpback whales have turned into a tourist attraction which has grown substantially over the last few years leading to concerns about the carrying capacity of the island and the waters surrounding it. Potential harassment of whales by water users could lead to the disruption of reproductive and social activities and, ultimately, displace the animals from the area. Whale-watching has become an important part of the local economy and the need to protect the humpbacks has become a necessity, not only to insure that the humpback whales are protected, but also to provide income to a coastal community in a developing country. The main aim of this study is to determine population size, habitat utilisation and behaviour patterns of humpback whales in the Machalilla National Park. It is also designed to investigate the influence of the newly-developing whale-watching industry on the humpback whales and on the local communities and to provide a basis for future management of this species in Ecuador. The thesis is structured in five chapters, which all include a short introduction and discussion. The chapters are preceded by a general introduction and a presentation of the methods used. In the first chapter the first abundance estimates for the Ecuadorian humpback whale population are presented and the occurrence and occupancy of individually-identified whales derived from photoidentification data are shown. In addition, the influence of the 1997/98 El Niño phenomenon on the humpback whales relative abundance and behaviour is illustrated and discussed. In the second chapter, the small-scale habitat use of humpbacks in their breeding ground is investigated using the example of the marine area surrounding the Isla de la Plata. With the obtained information core habitat for this species is proposed. The third chapter deals with particular aspects of a breeding ground, such as the importance of surface active behaviour for humpback whales and interactions with potential predators, such as orcas or false killer whales. It is discussed to which extend the 2

7 1. GENERAL INTRODUCTION Machalilla National Park is a typical breeding ground compared to other breeding grounds in the world. In the fourth chapter, observations made from the island on interactions between whales and whale-watching vessels are analysed. The short-term changes in behaviour are used to determine if and, how much, whale-watching can negatively influence humpback whales. The fifth chapter sets out the potential conflicts between the increasing commercial use of humpbacks by tourists involved in whale-watching. Using data from the previous chapters and including the specific problems of a small coastal community in a developing country, a base for a management concept for the marine area of the Machalilla National Park is proposed. The thesis ends with a general discussion and conclusions which can be drawn from the work. 3

8 2. STUDY AREA 2. Study area 2.1. GENERAL STUDY AREA The study area is extending from S to S, limited in the west by the Isla de la Plata (81 06 W) and in the east by the Ecuadorian coast. It is a large bight that forms part of the continental shelf with an approximate length of 25 and a maximum width of 20 nautical miles (Figure 1). The sea bottom is mostly made up of sand, gravel, rocky areas and coral reefs (Ayón 1988). Beyond the Isla de la Plata the continental shelf drops down rapidly to depths of more than 3000m. The study area is influenced by several large current systems. During the dry season (June to September), the Ecuadorian counter-current arrives from the west somewhere between 4 and 10 N and is deflected by the continent so that it splits into the north and south ecuadorial currents. Another large current is the Humboldt Current which arrives from the south. It forms the ecuadorial front when it meets the south ecuadorial current. During the dry season this front lies in the study area between 1 and 5 S and is characterised by moderate salinity and a high quantity of nutrients (Anonymous 1997). The waters show a high zooplankton and fish density and support a local fishing industry suggesting that the bay exhibits a level of primary productivity that is atypical of tropical marine systems (Anonymous 1997). From May to September the trade winds are regular and blow from the south-east. Isla de la Plata 1 17 S 20m 30m 50m Colombia studyarea # Ecuador 100m #Y Pto. Lopez #Y Salango Peru W Figure 1. Map of the study area 4

9 2. STUDY AREA 2.2. ISLA DE LA PLATA The Isla de la Plata (81 04 W, S) belongs to the Machalilla National Park (Figure 2). The island is covered in part by a dry coastal forest and is a breeding place for a variety of sea birds, such as magnificent frigatebirds (Fregata magnificens), blue-footed (Sula nebouxii), red-footed (Sula sula) and masked boobies (Sula dactylatra), and waved albatrosses (Diomedea irrorata). Originally it was free of terrestrial mammals but goats, cats and rats have been introduced by man. Other marine mammals around the island are several male Galapagos sea lions (Zalophus californianus wollebaeki) which arrived at the island around 1990 and since then have stayed. During 1998 a group of 18 Galapagos fur seals (Arctocephalus galapagoensis) used a bight in the north of the island, apparently breeding, but they left again in the same year. %a Faro (65m) N Bahia Drake %a Machete (80m) Palo Santo 1 km Escalera (90m) %a Figure 2. Map of the Isla de la Plata in the Machalilla National Park Tourist vessels arrive at the north of the island in the Bahia Drake where they anchor while the tourists visit the island. Two walks are open for the public, both with a length of about 5 km and a duration of about two hours. Two bights in the northern part of the island are used to conduct snorkeling. The bight Palo Santo and the bight to the west of Bahia Drake, both of which consist of areas of coral growing on rocks (Figure 2). 5

10 3. METHODS 3. Methods The abundance of humpback whales in the Machalilla National Park was estimated using markrecapture (based on photo-identification) and strip transect methodology. To determine occupancy between and within years, as well as to determine changes in relative abundance, behaviour and group sizes, photo-identification was carried out. Habitat use of humpback whales was investigated using land-based simultaneous observations. A theodolite was used to observe interactions between whales and whale-watching vessels MARK-RECAPTURE In estimating animals populations by direct counts researchers may either try to count the whole population, or to count a known section of it and attempt to extrapolate to estimate the population as a whole. To obtain complete counts, even of known population segments, it is necessary that the whole group be available within a limited time and space. This is rarely possible with whales. One of the techniques developed to overcome this problem was the capture-recapture or mark-recapture method. The mark-recapture technique was first employed in a study of human demography in London, U.K., in 1662 (Ricker 1975). The principle of this technique is that marked individuals released into the population will be re-caught in numbers proportional to their abundance in that population. The size of the population can then be estimated from the proportion of marked to unmarked organisms in random samples from the entire population. In animals the marking can be done by attaching an artificial tag, such as in the banding of birds, by applying an indelible substance, such as painting insects, or by removal of part of the animal itself, such as toe clipping in small mammals (Hammond 1986). Since 1932, an international whale marking scheme has been in operation. This uses a standard mark, which consists of a numbered metal dart which is fired into the whale blubber from a modified shotgun humpback whales have been marked in this way in the Southern Ocean and, of these, 150 have been recovered. The recovery rate for humpback whales was remarkably low considering the very heavy exploitation to which this species was subjected. Recoveries were obtained when whales were processed on factory ships or land stations, and the records were therefore dependent on the reliability of collection by the operators. A number of tags were found as the whales were being cut up, but others were found only in the residue in the cookers in which the oil was extracted. In Japanese whaling operations about 60 to 70 % of marks were recovered (Doi et al. 1970). Because whaling of humpback whales is now banned a benign tool was found to estimate abundance using mark-recapture. Over the last few decades photographs of the natural markings of cetaceans, normally on their flukes or dorsal fins, have been used to identify individuals. The great advantage of this method is that animals do not have to be handled physically. Also the marks are 6

11 3. METHODS permanent and will not affect the animals behaviour in any way, so that survival probabilities are unchanged. The following two models for mark-and-recapture data were used to estimate population size. I. Closed population model (Petersen estimator) According to Seber (1982) the following assumptions must be met: 1. The population is closed. 2. All animals have the same probability of being caught ( identified ) in the first sample. 3. Marking does not affect the catchability of an animal. 4. The second sample is a simple random sample. 5. Animals do not loose their marks. 6. All marks are reported on recovery. Individuals are marked once and a single sample is taken some time later and examined for marked individuals. The proportion of marked animals recaptured in a sample of the population is equivalent to the proportion of marked animals in the total population, N. Marking should be restricted to a short period of time but the subsequent sample can be taken after an extended period, e.g., a year. However, the longer the period between marking and recovery, the more likely it is that some of the assumptions of the technique will be violated, particularly those relating to immigration, emigration, and recruitment. According to this procedure, the estimate of the total number of individuals in a population, is where n 1 is the number of marked individuals, n 2 the total number of individuals in the sample (marked and unmarked), and m 2 the number of marked individuals recaptured in the second sample. If sample sizes are small, the Chapman s (1951) modified estimator for sampling is used: If the population is closed (assumption 1) no mortality or reproduction is to occur between samples. If only a short time period lies between the two samples we can assume that this condition is valid. If this is not the case, however, an open population model must be used. 7

12 3. METHODS II. Open population model (Jolly-Seber) According to Seber (1982) the assumptions of the Jolly-Seber model are as follows: 1. Every animal in the population, whether marked or unmarked, has the same probability of being caught ( identified ) in the i th sample, given that it is alive and in the population when the sample is taken. 2. Every marked animal has the same probability of surviving from the i th to the (i + 1) th sample and of being in the population at the time of the (i + 1) th sample, given that it is alive and in the population immediately after the i th release. 3. Every animal caught ( identified ) in the i th sample has the same probability of being returned to the population. 4. Marked animals do not lose their marks and all marks are reported on recovery. 5. All samples are instantaneous. The Jolly-Seber Model estimates the population size for each sampling occasion except the first and last. The estimator for population size is based on two equations: an estimate of the total number of marked animals in the population at the i th sampling occasion, M i, and a general form of the Petersen estimate for the i th sampling occasion, Where n i is the number marked and m i is the number recaptured in the i th sample. The estimate M* i is obtained by assuming that two groups of animals, those marked at time i, the s i, and those marked up to, but not including, time i, the (M i m i ) and r i of the s i are recaptured after time i. This leads to the relation: and Substituting the above into the generalised Petersen estimate, we obtain 8

13 3. METHODS Most mark-recapture studies on cetaceans have used closed population models due to the small number of samples necessary to obtain an estimate. One of the main problems with this is the assumption that no animals are born or die between the sampling. An open population model corrects for this, but if the population is small will lead to a large uncertainty of the estimate. The problems of applying the different models to the data in the current study will be discussed later. The calculations for the open population estimates were done using a software package (Krebs 1998) STRIP TRANSECTS Transect methodology was developed especially for cetacean species that were dispersed widely and were not useful for mark-recapture. Basically, a strip transect is a representative sample of a larger habitat. The numbers obtained in this sample are extrapolated for the whole study area. Variations of this technique are the distance sampling procedures of line- or point-transect sampling. In a strip transect survey the sighting platform (ship or aircraft) moves along each transect and records the number of targets (n) sighted within a predetermined distance (W) of the trackline. If all targets within the strip are certain to be detected then the effective search width (esw) is equal to the strip width used on the survey, W (from the trackline to the strip boundary). Suppose the total track length is L units, the study area surveyed A square units and the track is designed to give uniform coverage. This gives us: which is the usual estimate of abundance derived using the concept of mean density. Generally strip sampling is only used when alternative methods, such as line transects, cannot be used. In this study strip transects were used because the sightings were made from platforms of opportunity (whale-watching vessels) and the measurement of perpendicular distance to each sighting, needed for line transect, was not feasible PHOTO-IDENTIFICATION Life history and population information can be established for pinnipeds, cetaceans, and manatees using photographic techniques to identify individuals based on patterns of scars, natural pigmentation, callosities, or barnacle patches on the skin. Humpback whales can be identified 9

14 3. METHODS individually from the uniqueness of the coloration, shape, and scarring pattern of the ventral side of their flukes (Katona et al. 1979). Photo-identification was normally carried out from whale-watching vessels leaving from the small coastal town Pto. Lopez to go to the Isla de la Plata. The boats were 6m to 8m long with 75 or 115 horsepower engines. The number of tourists on each boat varied between ten and twenty. The photos were taken from the roofs of the vessels at a height of about 2 meters. The pictures of the flukes were taken with a 35mm single-lens reflex camera equipped with a 300mm lens or 70 to 210mm zoom lens. 200 ASA slide film was used. For each sighting of a whale or group of whales, time, GPS position, behaviour, group composition, group size and the pictures taken for each animal were recorded. Each day the sea state, swell height, cloud cover and visibility was noted. Photos of humpback whale flukes in the Machalilla National Park were taken from 1996 through Within a season, whenever possible, daily trips were made to conduct photo-identification. The effort in 1996 was concentrated in the months of August and September with a total of 28 boat trips conducted. In 1997 the field season did not start before late-july and ended in September with only 36 trips being made. In 1998 and 1999 sampling took place from June to September with 40 and 42 trips respectively. Only the years 1998 and 1999 were used for the analyses of group composition. For analyses of relative abundance, behaviour and group sizes, only the 1999 data was used because the effort took place from June 10 th to September 18 th, covering the greatest time span and thus giving a better idea of the migration pattern of the humpback whales. From 1996 to 1999 more than 3000 photographs of humpback whales were taken. Of these around 300 photographs were shots of flukes. In the later analyses all fluke photographs were judged to be of either good, fair or poor quality. Good and fair- quality photographs showed at least 50 % of the fluke at an angle sufficiently close to the vertical to distinguish the shape of the flukes trailing edges. For this study, poor-quality photographs were deleted from the data set. The best photograph of a fluke taken during one observation was assigned an identification number. During the matching of fluke photographs, a whale that was identified on more than one occasion was assigned an animal number, allowing us to reference all fluke identifications of that individual. All fluke photographs of good or fair quality were scanned with a slide scanner and stored in a data file together with the additional information available for that sighting SIMULTANEOUS OBSERVATIONS Three points on the island were used as bases for hourly scans. In the north-west Faro at a height of 65m, in the south-west Machete at a height of 80m and in the east Escalera at a height of 90m (Figure 2). At each observation point one to two observers would conduct hourly scans from 10

15 3. METHODS 9h00 to 16h00. To avoid bias in observation quality the observers were changed, randomly, every day. In 1998, the last week of June, July, August and September was used for observations. The positions of the sightings were noted using a ruler and a compass. The ruler was held at a perpendicular angle and a distance of 50cm to the eye and the upper mark was aligned with the horizon. The vertical angle to the sighting was calculated using the scale of the ruler and the height of the observation point and observer. The horizontal angle to the sighting was obtained using the compass. For each hourly scan, group size, group composition, behaviour and swim direction of the humpback whales were noted. Only sightings seen during the scan were noted. Any animals entering the field of vision after the end of the scan were ignored. In the subsequent analysis the areas of observations were separated into three adjacent areas that did not overlap (Figure 3). Only sightings of one observation point in these areas were permitted for analysis thus preventing a potential double sighting. To determine the spatial distribution of humpback whales at one point in time the data was analysed separately. For this, the distances for sightings from Escalera that were taken during one scan (e.g. at 10h00) were calculated. The distribution of distances between sightings was compared for sightings which included breaching animals in comparison to the distribution of distances between sightings of travelling or resting groups K K K K K K K K K K K K K K Observation range from Faro "8 Observation range from Machete "8 K K K K K K "8 Observation range from Escalera K K K K K K K K Figure 3. Isla observation points and range 3.5. HABITAT CHARACTERISTICS The study site was partitioned into 500 x 500m squares. The area measured 14 x 14km with the island in the centre. The maximum sighting distances were 15km from the island, but because the 11

16 3. METHODS sighting probability decreased with distance, only the sightings seen within the chosen area were used, so that equal coverage of the whole site could be guaranteed. The information on depth and substrate type was collected during several trips in which sonar was used. On selected sites the substrate was investigated using scuba diving (self-contained underwater breathing apparatus) equipment. Additionally, interviews with local fishermen were conducted. Figure 4 shows the substrate characteristics around the island. For each 500x500m square the dominant substrate type was defined as mainly rock or coral, mainly sand, mainly gravel or a mix of rock/coral and sand ' ' N 9 ' ' ' ' r 9 ' ' r r 9 ' ' ' ' ' ' rocks and coral with sand mostly sand rocks gravel coral Figure 4. Substrate type found in the marine area around the Isla de la Plata. For each 500x500m square the dominant substrate type is shown. 12

17 3. METHODS ' ' N 9' ' ' ' r 9' ' r r 9' ' ' ' ' ' depth in meters Figure 5. Characterisation of depth in the marine area around the Isla de la Plata. Depth information obtained from the transects (using the sonar) was complemented with the official sea chart of the Ecuadorian navy (INOCAR - Instituto Oceanográfico de la Armada 1984). Figure 5 shows the depth in the grid overlaying the marine area around the Isla de la Plata. For each 500x500m square the mean depth was calculated and later pooled into depth categories. 13

18 3. METHODS The sea state was obtained by observations from the island and was recorded in angles (e.g. 100 to 150 sea state 2 and 150 to 200 sea state 3). The area to the south of the island was generally 1 to 2 seastates (Beaufort scale) rougher than the northern part in the lee of the island. Due to the regular current system throughout the season this classification of higher sea states in the southern region did not change. This area was labelled exposed in contrast to the northern part which was called sheltered ( Figure 6) ' ' N 9' ' ' ' r 9' ' r r 9' ' ' ' ' ' sheltered exposed Figure 6. Characterisation of habitat type with regard to exposure (exposed or sheltered) in the marine area around the Isla de la Plata. 14

19 3. METHODS The area of the island took up 22.5 squares, each of 500m². The rest of the area could be separated into the habitat types shown in Table 1. The total size of the area surveyed was 381km². Table 1. Habitat types in the grid around the Isla de la Plata habitat number depth (m) substrate exposure number of 500mx500m squares number of 250mx250m squares size (km²) coral and/or rock sheltered coral and/or rock exposed coral and/or rock sheltered coral and/or rock exposed gravel sheltered gravel exposed gravel exposed rock, coral, sand sheltered rock, coral, sand exposed rock, coral, sand sheltered rock, coral, sand exposed rock, coral, sand sheltered rock, coral, sand exposed rock, coral, sand exposed rock, coral, sand exposed sand sheltered sand exposed sand sheltered sand exposed sand sheltered sand exposed sand sheltered sand exposed sand exposed Total size of the area 381km² 15

20 3. METHODS 3.6. THEODOLITE TRACKING OF WHALES The eastern point of the Isla de la Plata proved to be ideal to observe whales as well as whale - watching vessels. The height of the observation point (Escalera) allowed long-range observation of several pods of humpback whales without influencing the behaviour of the animals. Groups of whales seen were tracked using a WILD theodolite (with automatic vertical index) mounted on a tripod. The height of the observation point was obtained using a detailed map of the island provided by Fundación Natura, Ecuador. The focal plane of the theodolite could be established as 91.5m above mean sea level (which includes the height of the theodolite). Vertical and horizontal angles at each theodolite reading were measured to the nearest 20 seconds and the time was recorded to the nearest second. For each position the behaviour, group size and group composition (number of calves present in a group) were noted. Using the vertical angle to the sighting and the known height of the observer the distance from the observation point at sea level to the sighting could be calculated (a in Figure 7). In conjunction with the bearings obtained from the horizontal angles, the position of the whales relative to the observer could be calculated. The later computer analyses calculated the linear distance and bearing between successive fixes and the speed of movement. Approximate fixes (those made on the footprint left by the whale, for instance) were omitted from all calculations. Changes in height of the water level were not taken into account due to the small tidal movements in the study area. Figure 7. Use of theodolite from observation point Escalera on the Isla de la Plata. The height from the water surface to the observer (h) was determined to be 91.5m (focal plane). Distance to the sighting (a) was calculated using this height and the vertical angle given by the theodolite (α). 16

21 3. METHODS The speed of movement of a sighting was calculated by using the distance between two points and the time needed to cover this distance. The course of a group of whales was calculated dividing the total distance covered from position to position by the distance between the first and the last position. This number is 1 if the animals moved in a straight line and higher when the animals were less straight (more deviating) MAP PROJECTIONS, STATISTICAL ANALYSES AND SOFTWARE USED Maps Maps were either presented as nautical maps (degrees South and West) or as a UTM (Universal Transverse Mercator) projection for zone 17 (78 W to 84 W). In a UTM grid the world is divided into 60 north-south zones, each covering a strip 6 wide in longitude. In each zone, coordinates are measured north and east in metres. The northing values are starting with zero at the South Pole and reach 10,000 at the equator. A central meridian through the middle of the 6 zone is assigned an easting value of 500,000 meters. Values to the west of this central meridian are less than 500,000; to the east, more than 500,000. Thus in the maps presented here the x-axis represents the distance in metres from the central meridian of zone 17 (81 W) and the y-axis represents the distance in metres from the South Pole. The maps were generated using the software program ArcView GIS from ESRI (Environmental Systems Research Institute Inc.), version 3.2a. Statistical analyses All tests used were non-parametric. All tests were two-tailed and the significance level was set at Statistical software used was Systat 6.01 SPPS.Inc INTERVIEWS Interviews were conducted with local fishermen and guides to determine the presence of orcas (Orcinus orca) in the marine area between the mainland and the island. All interviews were made over one season and the name of the interview partners was noted to prevent double interviews. Because, in the years of the study, a program of environmental education including the fishermen was launched, further information was brought to the research team. This included special observations of humpback whales, such as a birth or a by-catch. Additionally local fishermen were interviewed with respect to the substrate types found around the Isla de la Plata. 17

22 3. METHODS 3.9. DEFINITIONS Relative abundance: The number of whales per hour searched by the whale -watching vessel. Sighting rates only include whales that were observed for a period of time after the initial sighting. It does not include whales seen in the distance or passed. The search effort does not include the time spent with a sighting, only the time actively searched by the researcher. As a result the sighting rates given here represent minimum values. Sighting: A sighting was defined as either a lone whale, or a group of whales where members of the group were within 100m of each other and generally moving in the same direction and coordinating their behaviour (Mobley and Herman 1985). Calf: A calf was defined as an animal in close proximity to another whale (less than one whale length separating the pair), and estimated to be less than 50% of the length of the accompanying animal. Occupancy: Occupancy was defined as the period, in days, between the first and last sighting of a whale in a season. Occupancies were calculated only for whales seen on at least 2 days in a season. The interval between the first and last identification of an individual whale provided a minimum estimate of its occupancy in the study area. Specific behaviour categories: milling : A group of whales surfacing regularly in different directions in the same area. socialising : This behaviour included any behaviour which was not agonistic or surface active, such as multiple animal posturing, parallel position of two animals, dorsal position (one animal on its back), singing, headstand and spy-hop. resting : Slow swimming of one or more whales with regular surfacing intervals or surfacing on more or less the same position without any abrupt or fast movement. travelling : Directional swimming with regular surfacing intervals at a moderate or fast speed. surface active : One or more whales engaged in activities such as breaching, flipper or fluke slapping, head slamming, tail breach ( lob tail ), fluke and flipper waving. agonistic behaviour : Any agonistic behaviour directed towards another whale including headlunges, breaches, fluke and flipperslaps. 18

23 3. METHODS General behaviour categories: reproductive behaviour : All surface active and agonistic behaviours were pooled together with socialising and milling behaviour into this category. travelling : Directional swimming with regular surfacing intervals at a moderate or fast speed. milling/socialising : All milling and socialising whales were pooled in this category. resting : Slow swimming of one or more whales with regular surfacing intervals or surfacing on more or less the same position without any abrupt or fast movement. Sea state: Determined by observation of the sea surface. 0 water surface was like a mirror, 1 some parts of the surface showed ripples, 2 waves all over the surface, 3 some waves showed whitecaps, 4 frequent whitecaps, 5 the whitecaps were carried away by the wind. Cloud cover: The cover of clouds was expressed in parts of 8. This means that 0 of 8 is a cle ar sky without any clouds and 8 of 8 a sky totally covered with clouds. Swell height: The height of the waves was estimated by observers using the bow of the boat as well as the highest point of the boat (1.5m). Visibility: Visibility was considered good if the horizon could be seen clearly and there was no rain or drizzle. Visibility was medium if some clouds or fog could be seen along the horizon or there was a slight drizzle. Visibility was poor if the horizon was not visible or it was raining. An X for visibility meant that the observers could not see more than 100m around the vessel (or less than 100m around the island) and observations were stopped. 19

24 20

25 4.1 ABUNDANCE AND DISTRIBUTION 4. Chapters 4.1. ABUNDANCE AND DISTRIBUTION 21

26 4.1 ABUNDANCE AND DISTRIBUTION Introduction As mentioned before, only very little information is available on the abundance or distribution of humpback whale stocks in the southern hemisphere. Before the onset of commercial whaling the number of humpback whales in the Southern Ocean was estimated to lie around 100,000 (Nowak 1999). In the 20 th century humpback whales were hunted close to extinction and Curry-Lindahl (1972) estimated that in 1965 less than 3,000 animals were left in the Southern Ocean. Information on population size and stocks in the eastern Pacific is scarce but would be essential to monitor a possible recovery of humpback whales, as has been documented for the African east coast (Findlay and Best 1996) and the Australian east coast (Chaloupka et al. 1999; Paterson and Paterson 1989). The only well known breeding area for humpback whales in the tropical East Pacific on the west coast of South America lies around the Gorgona Islands in Colombia. Estimates for this population range between 170 to 450 animals (Flórez-González 1991) and re-sightings with Antarctic humpbacks have confirmed that these animals migrate from Antarctic waters (Stone et al. 1990). Humpback whales have also been sighted around Coco Island in Costa Rica (Acevedo and Smultea 1995), Panama (Flórez-González et al. 1998) and the Galapagos Islands (Godfrey Merlen, pers. comm.) though it is not known whether these areas are used for breeding. Flórez-González et al. (1998) suggested that the humpback whales seen on the Ecuadorian coast only pass through the area while migrating to Colombia or possibly use the whole tropical East Pacific as a wintering ground, rather than being confined to a specific breeding site in Ecuador. While it is difficult to determine absolute population size with satisfying precision for whales, relative abundance can be useful to monitor local changes in occurrence. At the beginning of 1997 a weakening and reversal of the trade winds in the western and central equatorial Pacific led to the rapid development of unusually warm sea-surface temperatures along the South American coast (McPhaden 1999a). The height of what was to be the strongest El Niño event ever recorded (Wang and Weisberg 2000), was reached in December 1997 with sea surface temperature anomalies being the highest ever witnessed along the equator in the eastern Pacific (McPhaden 1999b). Temperatures started to level off again from May to September 1998 (CPPS 1998) and the colder sea surface temperatures typical of La Niña began (CPPS 1998). The biological effects of ENSO (El Niño Southern Oscillation) are normally based on a change in up-welling. The reduction of nutrients in the water column interrupts the recruitment of planctonic organisms, such as crustacean larvae (Moreno et al. 1998) and subsequently also effects the survival of top predators of the food chain, such as marine mammals. The influence on pinniped populations can be especially devastating, as was shown during the previous ENSO event in 1982/83 for the Galapagos fur seal (Arctocephalus galapagoensis) and the Galapagos sea lion (Zalophus californianus wollebaeki) (Limberger 1990). Only limited information is available on the influence of El Niño events on the distribution or abundance of cetaceans. The distribution of small odontocetes has been shown to change with the varying food availability due to an El Niño 22

27 4.1 ABUNDANCE AND DISTRIBUTION event (Shane 1995), but these species are able to move with their food resources and no increased mortality could be observed. The situation for a migrating species such as the humpback whales is different because this species, once in their breeding ground, do not feed (Chittleborough 1965), and thus does not depend on an intact food chain to survive. The 1997/98 El Niño phenomenon occurred during the ongoing study and thus gave an opportunity to investigate if and how this phenomenon would effect the occurrence and behaviour of the humpback whales. Objectives of this chapter: How are the humpback whales in the Machalilla National Park distributed in the study area, how long do they stay within a season and do they return from year to year? How large is the population of humpback whales in the study area? Did the 1997/1998 El Niño phenomenon have an effect on the occurrence or behaviour of the humpback whales? 23

28 4.1 ABUNDANCE AND DISTRIBUTION Results Distribution of humpback whales in the Machalilla National Park From the years 1996 to 1997 the search effort for humpback whales was concentrated between the Isla de la Plata and the towns Pto. Lopez and Pto. Cayo on the mainland. Figure 8 shows the distribution of humpback whales for all sightings where a position could be taken and using all years combined. Generally, animals concentrate in shallow areas of less than 100m depth, especially around the island. 1 22' S ÿ #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0#0#0 #0 #0 #0#0#0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0#0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0#0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0#0 100m #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0 #0#0 #0 50m #0 #0 20m 30m #0 ÿ 80 54' W Figure 8. Distribution of all humpback whale sightings made from whale-watching vessels from 1996 to 1999 in the Machalilla National Park Abundance of humpback whales in the Machalilla National Park Mark-recapture Five humpbacks were identified individually between years using photographs of their flukes. The sighting history of these animals is given in Table 2. One animal (C97-12) was identified in each year. Population size for the humpback whales was estimated using two mark-recapture analyses. First, Chapman s modified estimator for the Petersen model was used to calculated the population size between years (Table 3). Estimates for this closed population model vary between 144 to 405 animals using the combination of all years (1996 to 1999). Second, the Jolly-Seber model for multiple recaptures of open populations was applied. The population estimates were 85 and 276 animals for the years 1997 and 1998 respectively (Table 4). 24

29 4.1 ABUNDANCE AND DISTRIBUTION Table 2. Sighting history of the five whales identified between the years 1996 and X marks the year in which an individual whale was sighted. Id # whale C96-8 X X C96-10 X X C96-13 X X C97-4 X X C97-12 X X X X Table 3. Calculated population estimates using the Chapman estimator between years. The numbers in brackets are the 95% confidence interval. The estimates printed bold are those made from one year to the next (80 380) 289 ( ) 279 ( ) (78 385) 209 ( ) ( ) Table 4. Results from the Jolly-Seber open population model. The population estimates (N) and their confidence interval are given. N 95% C.I

30 4.1 ABUNDANCE AND DISTRIBUTION Strip-transects In 1999, strip-transects were used as a second method to estimate the local abundance of humpback whales in the Machalilla National Park. The transects from Pto. Lopez to the Isla de la Plata were considered a representative strip sample for the whole study area. The transects covered areas of low sighting density (the trajectory from Lopez to about 10km off the island) and high density (the area to the east of the island). During these transects we assume the strip width to be 1km on each side of the vessel. In this strip we assume that we will sight all humpback whales present if they are at the surface. Therefore an unknown proportion of sightings is missed and the numbers derived from this method are underestimates of the true population size. The two week period from July 9 th to July 28 th was used for the calculations because it is the time when the relative abundance of humpback whales is highest during the season (see Figure 11). During this time a mean of 0.26 whales/km² was sighted (range: from the minimum of 0.05 whales/km² to the maximum of 0.35 whales/km²). The total study area was considered the area limited in the east and north by the Isla de la Plata and in the south by Salango. This area is around 1,100km². Extrapolating the density of 0.26 animals per km² the population estimate for the humpback whales is 286. Using the minimum and maximum densities from the surveys, the error range of this estimate lies between 55 and 385 animals. Obviously the strip-transect can only be an approximation of how many whales can be found in the study area at the time of highest relative abundance. Nevertheless the numbers back up the estimates obtained by the mark-recapture estimates. Cumulative identification Using the photo-identification data, a third method can be used to calculate the number of whales in a population. For this method it is assumed that all animals will be identified at some point in the future. Thus one would expect to get fewer and fewer photo-identified animals each year, until only the newly born animals of each season are registered each year. In this manner one could obtain a curve that should begin with a steep incline and then level off to a near constant number of animals newly identified each year. In Figure 9 we can see the cumulative identification of humpback whales in months from the years 1996 to The linear increase of newly-identified animals indicates that the true number of animals in this population is clearly higher than the number of animals identified so far. A longer study period and a higher number of identified whales is needed to calculate the point at which the curve levels off. Nevertheless, the minimum number of animals in this population equals the total number of whales identified, this being 93 whales so far. 26

31 4.1 ABUNDANCE AND DISTRIBUTION 120 number of identified whales date (mm-yy) Figure 9. Cumulative number of newly-identified humpback whales per month in the years 1996 to 1999 using their flukes Occupancy and occurrence of humpback whales in the MNP Within-season occupancy Figure 10 demonstrates the maximum occupancy of the 12 individuals that were re-sighted within a season (only the maximum occupancy is shown even if an individual was seen several times). In 1997 one individual humpback whale was first photographed August 26 th, again August 31 st, September 23 rd and September 24 th. 3 number of animals days Figure 10. Observed maximum occupancies (number of days between first and last sighting) of humpback whales sighted on more than one day in the Machalilla National Park during 1996, 97, 98 and 99. Maximum occupancy was 30 days. 27

32 4.1 ABUNDANCE AND DISTRIBUTION Table 5 summarises data on effort and on occupancy of individual whales during the period 1996 to Observed occupancy of individuals ranged from 1 to 30 days; the mean occupancy for all whales observed in a year varied from 7 to days, with an overall mean of 13 days. Table 5. Number of cruises made, number of individuals photographically identified, mean occurrence (in days) of individuals, and maximum and mean occupancy (in days) of individuals for each year and study period All years No. of cruises No. of individuals No. of newly identified animals Mean occurrence Occupancy mean max S.D

33 4.1 ABUNDANCE AND DISTRIBUTION Migration patterns of humpback whales in the MNP Changes in relative abundance The relative abundance of whales was calculated as the number of whales per hour searched by the vessel. The photo-identification carried out in 1999 ranged from June to September, spanning the whole reproductive season of the humpback whales. The relative abundance calculated from the transects varied from a minimum average of 0.3 animals/hour on June 17 th to a maximum of 7.2 animals/hour on July 23 rd. Figure 11 shows the increase in whale abundance in mid/late June and again a decrease of abundance in the beginning of September. Figure 11 shows how the changes in relative abundance mirror the migration pattern of the humpbacks whales/hour to to to to to to to Figure 11. The seasonal changes in relative abundance of humpback whales throughout the 1999 season. Relative abundance is represented by the average number of whales seen per hour in each two-week period (error bars represent S.D.). Swim-direction For a total of 278 sightings the swim direction was determined using a hand-held scuba-diving compass. The distribution of swim directions of all travelling sightings in 1998 was compared for the months June-July and August-September. The distributions are not significantly different (χ²test; p=0.09). Figure 12 and Figure 13 show the distributions obtained. In the early season most animals travel between 90 (east) and 255 (south-west). In the late season most animals travel in a southerly direction (135 to 285 ). The northern swimming directions expected from the early season when animals arrive from their feeding grounds could not be observed. 29

34 4.1 ABUNDANCE AND DISTRIBUTION % swim direction Figure 12. Distribution of swim directions of travelling humpback whales seen in June and July The swim directions are given in degrees on a compass (e.g. 180 animals swimming south). 25 % swim direction Figure 13. Distribution of swim directions of travelling humpback whales seen in August and September The swim directions are given in degree on a compass (e.g animals swimming east). 30

35 4.1 ABUNDANCE AND DISTRIBUTION To determine whether the expected northward migration in the beginning of the season could be detected, the distribution of swim directions for the single months was considered. Figure 14 shows the distribution of swim directions for the four months, June, July, August and September. The swim directions are shown in 10 steps and the percentage of sightings seen in each category is given. Even though the distribution changes slightly throughout the season, hardly any animals are seen swimming in a northern direction at any given time June July August September Figure 14. Percentages of travelling humpbacks for each 10 swimming directions in the months June to September The graphs represent a compass (e.g. 0 correspond to swim direction north). 31

36 4.1 ABUNDANCE AND DISTRIBUTION The influence of the 1997/1998 El Niño Southern Oscillation Changes in relative abundance Table 6 shows the effort in the month of August in the different years and the number of flukes identified, as well as number of whales and number of sightings seen. Although the effort was very high in 1997, the number of animals seen per hour searched was the lowest (Figure 15). The number of humpback whales identified through their flukes in the years 1996 to 1999 showed a similar trend to that of the relative abundance. In 1997 only 14 humpback whales could be identified by fluke photographs although the effort was highest in this year (Table 6). whales/hour 3,5 3 2,5 2 1,5 1 0, effort in hours whales / hour effort (hours searched in August) Figure 15. Relative abundance of humpback whales and search effort in the month of August in the years 1996 to Table 6. Search effort (in hours), number of whales photo-identified, number of total sightings, number of total whales sighted and sightings and whales corrected for effort for the month of August in the years 1996 to hours flukes number of number of sightings whales per observed identified sightings whales per hour hour

37 4.1 ABUNDANCE AND DISTRIBUTION Changes in group size and composition The distribution of group sizes did not differ significantly between the years 1996 to 1999 (χ² -test; p=0.97). The mean group sizes were 3.16 (1996), 1.96 (1997), 2.6 (1998) and 2.4 (1999). Modal group size was 2 for all years. The percentage of calves in relationship to all whales seen in August differed between 2.2% (1996), 6.5% (1997), 3.6% (1998) and 6.6% (1999). Due to the low number of sightings which included calves a statistical comparison between years was not possible. percent of sightings or 2 3 or 4 5 or more group size Figure 16. Distribution of group sizes in the month of August from 1996 to1999. Changes in behaviour In Figure 17 we can see the distribution of behaviour categories observed in the month of August from 1996 to The behaviour of the humpback whales was put into one of the following categories: milling (including socialising), resting, surface activity and travelling. The behaviour of humpback whales did not show any significant change between years (χ²-test; p=0.18). percent of sightings milling resting surface active travelling Figure 17. Distribution of behaviour categories observed in the month of August 1996 to

38 4.1 ABUNDANCE AND DISTRIBUTION Relationship with temperature The relative abundance of humpback whales (whales/hour) in the month of August in the years 1996 to 1999 was inversely related to the mean sea surface temperature in the study area. In the years with normal temperatures of around 23 C about 3 whales were sighted per hour searched. In 1997 when mean sea surface temperatures were at 29 C, less than one whale was sighted per hour searched (Figure 18) whales/ hour y = x R 2 = SST C Figure 18. Relationship between sea surface temperature along the Ecuadorian coast (source: Climate Diagnostic Center) in August and the relative abundance of humpback whales. Equation of regression is shown in graph. 34

39 4.1 ABUNDANCE AND DISTRIBUTION Discussion Abundance When using mark and recapture models to estimate population size certain assumptions must be met. In case of the Chapman population model one of the assumptions is that the population is closed. To try to allow for the fact that the population is not totally closed (due to births and deaths occurring from year to year) I also applied the Jolly-Seber open population model. One of the assumptions for both models was that the samples taken are representative of the population. In 1997 only 12 new animals could be identified by their flukes although the effort was as high as in the other years. Due to the El Niño Southern Oscillation in 1997 the sea surface temperature in the study area was up to 10ºC higher than in normal years. It seems that either fewer humpback whales were present or that the animals changed their behaviour in a way that made them harder to see and consequently photograph. Therefore the samples from the year 1997 might not be representative of the population, thus violating one of the assumptions of mark and recapture models. For that reason the population estimate of 405 animals obtained from the closed population model for the years 1998 to 1999 seems to be the most useful for a preliminary abundance estimate for the humpback whale population of the Machalilla National Park in Non-El Niño years. The range of this estimate is also confirmed by the approximation of local abundance derived from the strip-transects which is very similar to the mark-recapture estimates. We should keep in mind that an increased effort and thus a larger sample size will hopefully provide us with a more precise estimate based on the photo-identification study in the future. Also several studies indicate that estimates in wintering grounds obtained via mark-recapture are not as precise as those obtained in feeding grounds (Baker et al. 1986; Cerchio 1998). It would therefore be helpful to include photos obtained from the feeding grounds in Antarctic waters in the mark-recapture abundance analyses of the Machalilla humpback whales. Occupancy The photo-identification data showed that individual humpbacks were not only seen from year to year but were also re-sighted within a given season. The maximum occupancy of 30 days, found for the Machalilla National Park, is very similar to the occupancy found in other reproductive grounds. In a breeding area in Hervey Bay, Australia two whales were seen in the area over longer periods, one of 13 and one of 19 days (Corkeron et al. 1994). In the waters of Virgin Bank, West Indies 17 whales identified in one year were sighted again in that season with 13 days between the sightings (Mattila and Clapham 1989). In a study on Silver Bank, West Indies, 9.1% of identified whales were sighted again in the same season; the greatest time between first and last sighting was 30 days and the mean period of residency of the whales was 8.52 days (Mattila et al. 1989). Individually-identified humpbacks have been sighted more than once over several weeks off Hawaii, but some of these sightings include large-scale movements. The longest sighting interlude was 44 days where an animal was first seen in Hawaii and then in Maui (Baker and Herman 1981). The photographic records at the island of Hawaii revealed re-sightings of a mother calf pair over a 26 day interlude and whales were re-photographed at interludes ranging from a few days to as 35

40 4.1 ABUNDANCE AND DISTRIBUTION long as 34 days. A study in Samana Bay, Dominican Republic (Mattila et al. 1994) showed the largest time period between identified whales within a season was 33 days. The estimates of the occupancy of humpback whales in the Machalilla National Park were considered minimum residence times because not all pods were sampled every day. Most whales spent a short period (up to 5 days) in the area, but 7% spent more then two weeks in the study area. Although it is possible that these animals left and re-entered the bay during that time, re-sightings of one single animal over 4 times within 30 days make this doubtful. The slightly bimodal distribution of occupancies suggests some whales established preferred ranges within the study area while others were relatively transient. Investigating the site fidelity to the humpbacks wintering grounds, Baker et al. (1986) found that of the 604 animals photographically identified in Hawaii between 1977 and 1983, only 83 (13.7%) were seen in more than 1 year. In the North Atlantic, Katona and Beard (1990) reported that only 6% of the animals photographed in the waters of the Dominican Republic were seen in more than one winter season, and only 6% and 1% were seen in more than 1 year in Puerto Rico and the Virgin Islands, respectively. Similarly, Mattila et al. (1994) reported that of 397 animals identified over four winter seasons in Samana Bay, Dominican Republic, only 18 (4.5%) were seen in more than 1 year. For the Machalilla National Park only 5 individuals of a total of 93 identified (4.65%) were seen again. One explanation for the apparently low levels of fidelity to the winter grounds is that some animals do not migrate to the winter grounds each year, but instead remain on the feeding grounds, or return before completing the migration. In some wintering areas, such as the waters of south east Alaska, humpbacks are sighted every month of the year (Straley 1990). Matthews (1937) describes humpback whales catches in the feeding grounds of the South Atlantic throughout the winter. Unfortunately, so far research effort on the feeding grounds has been relatively limited in the winter months due to the difficult weather conditions and limited daylight. Some indirect evidence that whales may overwinter comes from a biopsy study of humpback whales migrating past the east coast of Australia. Brown and Corkeron (1995) found the ratio of males to females was 2.4 : 1. The sex ratio at birth is approximately 1 : 1 (e.g. Chittleborough 1958; Glockner-Ferrari and Ferrari 1990; 1972), as well as the sex ratio in the summering grounds (Clapham et al. 1995). Craig and Herman (1997) conclude that the energy costs of migration and reproduction may deter some females from undertaking or completing the journey annually, and that conception may occur before arrival in the area traditionally associated with breeding, the impregnated female than discontinuing her migration and returning to the feeding area. From an energetic point of view this would be preferable for a female, because in addition to the spatially- and temporally-lengthy migration between summer and winter grounds they cannot feed in the winter. Dawbin (1966) suggests that mature females may follow a 3-year cycle: pregnancy, lactation, and then a period of resting. Seasonality in abundance Evidence that the study area is a breeding ground for humpbacks is given by the distribution of relative abundance. We can observe a typical migration pattern with the arrival of animals in June, the highest relative abundance during the peak season from July to August and the inset of the southern migration in September. Were this to be a non-breeding population, one would expect to 36

41 4.1 ABUNDANCE AND DISTRIBUTION see a higher number of whales during the migration periods June and September. Such a bimodal distribution for whales migrating past an area can be found on the west coast of South Africa (Best et al. 1995) as well as off Brisbane in Australia. Here peaks of abundance are found during the northward migration from June to July as well as during the southward migration from August to the end of October (Bryden et al. 1990). A typical distribution for a reproductive ground can be found in breeding areas such as Samana Bay in the Dominican Republic. Here Mattila et al. (1994) observed a peak of relative abundance of northern hemisphere humpback whales in February. Relationship with other areas in the eastern tropical Pacific Some humpback whales have been documented switching breeding grounds within the West Indies (Mattila et al. 1994), between Hawaii and Mexico (Darling and Jurasz 1983) and most recently between Hawaii and Japan (Salden et al. 1999). Salden et al. (1999) suggested that these wanderers are mainly males. Nevertheless, movement between wintering grounds is relatively rare compared to regional return (e.g. Baker et al. 1986). However, within a larger reproductive area, such as the Hawaiian Islands, extensive movement of individuals does take place. Cerchio et al. (1998) showed that individual humpbacks, mostly males, can move between the Hawaiian Islands Kauai and Hawaii in short time periods. In the tropical East Pacific one photo-identified humpback whale was sighted in Colombia and Ecuador, but not in the same year (Flórez-González et al. 1998). The distance between the Machalilla National Park and the Gorgona Island is about 325 nautical miles and could be travelled in about 10 days (using the migratory speed of 220 nautical miles per week calculated by Dawbin 1966 for humpbacks). It is thus possible that the Ecuadorian and Colombian humpback whales are part of a larger reproductive area in which some movement takes place. Bravo et al. (1994) note that humpback whales have been observed as early as mid-june in the Colombian breeding ground, their abundance peaking between August and October, and seen as late as mid-december. If the Colombian humpback population arrives in June in Colombia this could mean that at least part of the population passes through the Machalilla National Park during their northbound migration. A strong peak in relative abundance is apparent at the beginning of July, possibly indicating an overlap of these populations. However, if animals from the south pass the Machalilla area to continue to Colombia we would expect to find a peak in northern swim directions. Since this was not the case it seems probable that the migration route of the Colombian whales is further offshore. In this context it is interesting to note that the season at the Ecuadorian coast is from mid-may to mid-october, with humpback whales rarely sighted after the beginning of October. It is therefore improbable that the whales from the Colombian population pass through the Machalilla National Park on their southward migration. The whale-watching tours go to the Isla de la Plata throughout the year and record any sightings of cetaceans outside of the typical humpback whale season. One possible scenario is that at the end of the reproductive season the humpback whales of Colombia go west before starting south, possibly passing the Galapagos Islands. Here humpback whales are sighted from July to September, but only a few individuals are observed and no increase 37

42 4.1 ABUNDANCE AND DISTRIBUTION of sightings over time is apparent (G. Merlen pers. comm.). Further research, including the islands of Coco, Galapagos and the waters of Panama, are needed to understand the migration patterns of the humpback whales present in this area. El Niño Normally marine mammals are influenced by the Niño phenomenon because of an associated change in availability of prey (Arntz et al. 1990). Both, during the and ENSOs there were times of food shortage and increased mortality for pinnipeds. On the Galapagos Islands Galapagos fur seal pups (Arctocephalus galapagoensis) incurred 100% mortality during 1982 (Trillmich et al. 1991). In having mobile young, Cetaceans can react to food scarcity by changing habitat. However, since humpbacks do not feed at their breeding grounds, the lack of potential prey should not influence their abundance or distribution. Other factors must be responsible for the lower numbers of humpbacks seen in 1997 and 1998 in the Machalilla National Park. In the summer of 1997 we measured maximum sea surface temperatures of 32 C in the study area. All humpback whale breeding grounds are characterised by warm water (e.g. 24ºC to 28ºC in the West Indies (Naughton 1997)), but the particular high temperatures encountered in 1997 might well lie at the upper limit of the heat tolerance in humpbacks. Cetaceans are well adapted for minimising heat loss. Their large bodies present a relatively small surface and therefore they lose relatively less heat than small animals. Also, they have developed a thick insulating layer of blubber and their cutaneaous blood vessels are arranged in a way as to retain as much heat as possible by the body (Slijper 1962). Cetaceans, however, cannot lose surplus heat by perspiring, panting, or by increasing their rate of respiration. Their skin is not as vascular as that of other mammals (e.g. ears of terrestrial mammals) which loose heat via the blood. Tomilin (1960) suggested that rorquals have heat dissipation problems in warmer waters. When whales are more active they produce more heat, by up to a factor of ten (Kanwisher and Sundnes 1966). Humpback whales, especially the males, are very active while in the breeding grounds. Breaches, flipper and fluke slaps as well as aggressive interactions between whales are part of the normal behaviour. One method to compensate for the heat production during these behaviours, could be to increase blood circulation to the skin as well as the flippers, dorsal fin and flukes. Flippers protrude from the body envelope of blubber without fat covering and with little musculature for heat production and thus are effective cooling surfaces (Tomilin 1951; Irving 1969). Throughout the 1997 season we observed several animals with pinkish undersides of flippers and the ventral part of the bodies, which we assume was due to a higher blood circulation. If we assume that the higher temperatures are detrimental to reproductive behaviour we would expect to see fewer large competitive groups and a decrease in surface active behaviours. We could not observe any change in the behaviour or in the distribution of group sizes when the sea surface temperature increased. This however, might be harder to detect because we only noted surface 38

43 4.1 ABUNDANCE AND DISTRIBUTION active behaviour irrespective of, for example, the frequency of breaches or flipperslaps. It might well be that more detailed behavioural observations would have shown an effect. Other factors are related to El Niño events such as changes in salinity and the current systems so that we cannot rule out that changes in abundance of humpbacks my be due to another factor. Nearshore off Ecuador torrential rainfall increased the river discharge, turbidity and sedimentation of coastal waters. Some authors have suggested that an increase in turbidity can lead to a change in the distribution of humpback whales (Naughton 1997). It seems that the humpback whales in the Machalilla National Park changed their distribution, possibly staying in colder waters during the El Niño phenomenon in 1997 /1998. This was only a short-term displacement though because in 1999 the numbers of humpback whales were back to pre-enso levels. One reason for this displacement might be that, although the temperature in the study area was still tolerable, other areas with lower temperature were preferred by part of the population. Considering the global changes of temperature and their influence on the world oceans it seems important to find out more about the reasons for habitat changes in cetaceans. Conclusions: The marine area of the Machalilla National Park forms a reproductive ground for humpback whales. The first abundance estimate for this population lies by 405 animals (C.I.: ). The 1997/98 El Niño led to a temporary change in local abundance of humpback whales. 39

44 40

45 4.2 HABITAT USE 4.2. HABITAT USE 41

46 4.2 HABITAT USE Introduction In general, the distribution of cetaceans is strongly influenced by the distribution of their prey (Acevedo and Würsig 1991; Cockcroft and Peddemors 1990; Gowans and Whitehead 1995; Smith and Whitehead 1993) which aggregate in areas of high productivity. For example, dolphin abundance is significantly correlated with the abundance and distribution of prey. The dolphins move freely through the area, locate highly productive feeding areas, exploit them and then move on in search of new feeding areas (e.g. Defran et al. 1999). In contrast to terrestrial animals, the breeding and feeding activities of most cetaceans occur concurrently in the same waters. Cetaceans do not rely on structures such as nests or caves. The only exception to this are several large whale species, which migrate to special areas to breed and give birth to their young. Because these areas are remote from their feeding habitat their home range is impressive. Gray whales, for example, migrate several thousand kilometres from the feeding grounds in Alaska to their reproductive grounds in the Baja California (e.g. Darling et al. 1998). Humpback whales conduct the longest migration of all mammals, from productive high latitude regions used for feeding, to tropical and subtropical waters in coastal or insular regions used for breeding and calving (Stone et al. 1990). Although we know these areas are important for successful reproduction, the factors which influence the choice of these areas are still poorly understood. The general distribution of humpback whales and their migration pattern (Chapter 4.1) demonstrated that the marine area around the Isla de la Plata in the Machalilla National Park is frequently used during the reproductive season of the whales from June to September. The observations of behaviour and distribution patterns from an island are advantageous because the observers do not influence the animals as they do on a boat. As mentioned before, humpback whales do not feed in their breeding ground so their habitat use should not depend on the distribution of potential prey. Instead the physical characteristics such as exposure, depth or substrate type need to be taken into account. For humpbacks the inshore distribution while in their breeding areas renders them particularly susceptible to the effects of human activities in the coastal zone and general degradation of inshore habitats. An adequate identification of core habitats where biologically and socially important behaviours concentrate, is an essentia l part to understand the ecology and to gain insight on the environmental and behavioural determinants of the habitat use and preferences of humpback whales inhabiting the Machalilla National Park. Objectives of this chapter: Do humpback whales show a preference for a certain habitat around the Isla de la Plata? What are the characteristics of any preferred ( core ) habitat for humpback whales? 42

47 9' HABITAT USE Results Habitat use around the island Distribution of sightings in relationship to depth Figure 20 shows the distribution of all humpback whale sightings in the year 1998 as seen from the Isla de la Plata in relationship to depth. The underlying colours represent the depth around the island. 42% of the sighted humpback whales were in waters less than 30m deep, 48% in waters of 31-60m and 10% in waters over 60m. % of whales less than 30m 30 to 60m more than 60m Figure 19. Percentages of whales seen around the Isla de la Plata with regard to depth. 9' ' ' ' ' ' ' ' ' r r r 9' ' ' ' ' humpback whale group sizes >5 depth in meters Figure 20. Humpback whale sightings around the Isla de la Plata in 1998 (June-September). The size of circle indicates number of animals in a sighting. 43

48 9' HABITAT USE Distribution of sightings in relationship to substrate Figure 22 shows the distribution of all humpback whale sightings in the year 1998 as seen from the Isla de la Plata in rela tionship to substrate. The underlying colours represent the substrate type around the island. Rock and coral were combined into one category. 41% of humpbacks were in waters over a mix of rock/coral and sand, 28% were over gravel, 18% over sand and 13% over rock/coral substrate. % of whales gravel rock/coral rock/coral and sand sand Figure 21. Percentage of whales seen over different substrates around the Isla de la Plata. 9' ' ' ' ' ' ' ' ' r r r 9' ' ' ' ' humpback whale group sizes >5 substrate rocks and coral with sand mostly sand mostly rocks mostly gravel mostly coral Figure 22. Humpback whale sightings around the Isla de la Plata in 1998 (June- September) in relationship to substrate. The size of circle indicates number of animals in a sighting. 44

49 9' HABITAT USE Distribution of sightings in relationship to exposure Figure 24 shows the distribution of all humpback whale sightings in the year 1998 as seen from the Isla de la Plata in relationship to exposure. The underlying colours represent the sheltered or exposed around the island. 63% of humpbacks were in exposed and 37% in sheltered waters. % of whales exposed sheltered Figure 23. Percentages of whales seen around the Isla de la Plata with regard to exposure 9' ' ' ' ' ' ' ' ' r r r 9' ' ' ' ' humpback whale group sizes >5 exposure sheltered exposed Figure 24. Humpback whale sightings around the Isla de la Plata in 1998 (June- September) in relationship to exposure. The size of circle indicates number of animals in a sighting. 45

50 4.2 HABITAT USE Determination of core habitat To determine what part of the area around the island is important to humpback whales the abundance in the area, the observed behaviours as well as the presence of calves was used. Abundance Figure 25 shows the number of whales (per scan/km²) sighted in each of the squares in the study area. For the determination of core habitat all squares including more than 0.05 animals per scan per km² were selected. whales/scan/km² Figure 25. Distribution of humpback whale abundance around the Isla de la Plata (data from June to September 1998) 46

51 9' HABITAT USE Behaviour Figure 26 shows the different behaviours shown around the island; the behaviour categories were surface display, milling/socialising, resting, travelling and unknown. 9' ' ' ' ' ' ' ' ' ' r 9' r r 9' ' ' behaviour categories unknown travelling resting surface display milling/socialising Figure 26. Distribution of behaviour categories observed June-September 1998 around the Isla de la Plata 47

52 4.2 HABITAT USE The different behaviours were rated according to the importance to the humpback whales. Travelling was considered the least important behaviour to humpback whale reproduction and was thus not included. Surface active behaviour was not included as an important behaviour because many of the behaviours which occur in this category are not exclusively associated with reproduction but also occur in other contexts. Resting behaviour was considered important because humpback whales are not alert when they are involved in this behaviour and thus more susceptible to potential dangers (such as collisions with vessels). Also behaviour associated with milling/socialising was considered important to humpback whales because it is thought that during these behaviour categories the actual mating takes place. All squares in which resting and/or milling or socialising occurred was selected for core habitat ( Figure 27). occurrence of resting milling Figure 27. Occurrence of resting or milling/socialising behaviour of humpbacks around the Isla de la Plata 48

53 4.2 HABITAT USE Presence of calves Additionally all squares in which calves were sighted were included for analyses of core habitat ( Figure 29). Calves were only seen in 3% of all sightings around the Isla de la Plata. occurrence of calves Figure 29. Presence of calves in the study area around the island 49

54 4.2 HABITAT USE Core habitat To determine core habitat around the Isla de la Plata all squares which included at least two of the factors used high abundance, important behaviour, occurrence of calves - were included. The area has a size of 19.25km² (Figure 29). core habitat Figure 31. Determination of core habitat for humpback whales using distribution patterns, behaviour, presence of calves and residence times of humpbacks. Characteristics of core habitat Table 7 gives a summary of the characteristics of the core habitat as defined by substrate type, depth and exposure. The dominant substrate type is gravel, the dominant depth is less than 30m and the larger part of the area was exposed. Table 7. Characteristics of humpback whale core habitat depth (m) % substrate type % exposure % 0 to sand 10.3 sheltered to mix sand / rock / coral 30.8 exposed to rock / coral 20.5 > gravel

55 4.2 HABITAT USE Trackings In addition to simultaneous observations theodolite trackings of humpback whale sightings were conducted from the observation point Escalera in the east of the Isla de la Plata. Inspection of trackings of animals not accompanied by vessels showed that many trackings (a total of 11 were chosen because they were followed for several hours) not only passed the island but crossed in a small area of 1 x 1km² (marked red in Figure 30). The trackings were made in different years and months and the starting points of the tracking was always several kilometres away from the island. The four squares of 500 x 500m which were used so intensively are all characterised by waters of less than 30m depth. The upper left square has a rocky substrate, the upper right square has mostly gravel. Both are lying in sheltered waters. The lower two squares are exposed and have a rocky bottom. The border of exposed and sheltered waters is passing through the area. Some of the whales spent substantial time in this small area (as can be seen by the frequent positions on the trackings). The behaviours shown were variable but included resting and the headstand behaviour described in chapter 4.3. Several of the animals were possibly singing (staying underwater for up to 20 minutes, surfacing in the same area) but because a hydrophone was not deployed, this could not be confirmed Figure 32. Examples of 11 trackings of humpback whales in 1998 and The red box has a total diameter of 1km x 1km. The 500m x500m squares correspond with the squares defined in the habitat maps (see Methods). The four squares in the marked area are characterised by shallow water of less than 30m depth and hard substrate (gravel and rock). The area is lying at the border of sheltered and exposed waters. 51

56 4.2 HABITAT USE Discussion The humpback whales in the Machalilla National Park are generally found in a shelf area less than a few hundred meters deep (see chapter 4.1). Studies on other breeding grounds confirm that humpback whales prefer coastal, shallow waters within the 183m contour line (Chittleborough 1953, Herman and Antioja 1977, Winn et al. 1975). Forsyth et al. (1991) found that whales in the Penguin Bank and Maui regions were located at a mean depth of 94m. Recent aerial survey data in the same region showed that 74% of all pods were seen in waters less than 183m deep (Mobley et al. 1994). Frankel et al. (1995) also found a preferential usage of the shallower waters 183m for singing humpbacks. The observations from the Isla de la Plata showed a preference for even shallower areas. Here 90% of the sightings were made in waters with a depth of less than 60m. Hardly any whales were seen in depths of more than 90m. For the definition of core habitat the abundance and the behaviour of the humpback whales as well as the presence of calves was used. The resulting area lies to the east of the Isla de la Plata and is mostly defined by shallow waters less than 30m in depth - and substrate made up of gravel. The border between exposed and sheltered waters passes right through. From looking at the sightings of whales it seems obvious that this area is important, the problem is now to determine why. It is hard to imagine in what way this area should be better than other areas for socialising and milling and thus potentially mating. Humpback whales are adapted to live in waters of all depths and are sure to be able to conduct any behaviours needed for reproduction in deep waters as well as in shallow waters. A possible explanation for the observed resting behaviour might lie in the border between exposed and sheltered waters. From the observation point Escalera the observers could often see a foam-line on the water, indicating some kind of current system. This might be used by humpback whales to swim slowly and constantly without actually moving from their position. Hastie (1991) observed bottlenose dolphins staying in a relatively fixed position when feeding in a tidal current. If the whales swim constantly against a not too strong current this might be an effective way to rest without having to be too alert about the surroundings. However, more detailed studies on the currents in the area are needed to investigate this hypotheses. The number of calves observed in the core habitat or generally around the island were too few to come to general conclusions. There is evidence from other studies that females with calves preferentially use shallower or nearshore waters in both high- and low latitude ranges (Glockner and Venus 1983; Whitehead and Moore 1982). This may be to take advantage of calmer water, supposedly because these waters are easier for newborn calves to navigate in. In the tropics, shallow waters might also minimise the possibility of predation by sharks (Glockner and Venus 1983; Mattila and Clapham 1989; Whitehead and Moore 1982), or to avoid harassment by males (Smultea 1994). On a feeding ground in Massachusetts Bay, Clapham and Mayo (1987) found that mature females were more likely to be found in this inshore region in years when they had a calf than in years when they did not, but the reason for this apparent preference is unclear. In the 52

57 4.2 HABITAT USE Machalilla National Park it is possible that the areas with high breeding activities, such as the waters around the island are segregated from areas where mother-calf pairs are more frequent. One other hypotheses can be brought forward to explain the observed concentration of animals in the core area. While in their breeding ground humpback whales produce songs (Tyack 1981). These are thought to serve as a signal to other humpback whales (discussed in detail in chapter 4.3). The core habitat was not only shallow but also dominated by hard substrates such as gravel or rocks. The audibility of any sound underwater is determined, among other factors, by the sound propagation characteristics. Interestingly enough enhanced sound transmission can be expected when the bottom type is reflective, e.g. rocky, making sounds louder on a rocky bottom in a shallow area than on a sandy bottom. Again, further study including recordings in the core area are needed to determine if this might be true. Even if we can only hypothesise on why the humpback whales are concentrated to the east of the island, this apparent dependence on a small area within an already restricted inshore distribution makes them particularly vulnerable to alteration or loss of this habitat. The data collected here provide the basis for identifying core habitat within the marine area of the Machalilla National Park. Furthermore, this work represents a step towards understanding the dependence of these animals on the restricted, shallow-water, inshore marine environment and, as such, should be of value in other areas where there is little knowledge of humpback whales and their ecological requirements. Conclusions: 90% of the humpback whales around the Isla de la Plata preferred shallow waters of less than 60m in depth. Using abundance, presence of calves and the occurrence of important behaviours a core habitat for humpback whales around the Isla de la Plata could be described. A small area to the east of the island seems to be of special importance although the reasons for this need to be further investigated. 53

58 54

59 4.3 REPRODUCTIVE BEHAVIOUR 4.3. REPRODUCTIVE BEHAVIOUR 55

60 4.3 REPRODUCTIVE BEHAVIOUR Introduction As we have seen in the previous chapters the migration pattern, the return of humpback whales from year to year and within a season as well as their distribution in shallow waters, indicate that the Machalilla National Park is used as a reproductive ground. To obtain additional evidence that reproduction takes place we need to investigate the presence of new-born calves as well as characteristic reproductive behaviour. The most famous behaviour observed at breeding grounds is the humpback whale song (Tyack 1981). The concurrent singing of many whales may be a form of communal display by males (Herman and Tavolga 1980; Whitehead and Moore 1982) and, among other functions, may help to synchronise ovulation in females with the presence of mature males (Baker and Herman 1984; Herman and Tavolga 1980). Another typical behaviour is the forming of so-called competitive groups in which several males compete for access to a single female (Baker and Herman 1984; Clapham et al. 1992; Tyack and Whitehead 1983). A high level of aggression is seen, especially between escorts and intruding whales, and aerial behaviours such as breaches and flipper slaps are also frequent. Additionally several behaviours associated with mating have been described. Unfortunately mating has never been observed in humpbacks and it is assumed that it is either a brief interaction or that most of it happens well below the surface. The reason for some behaviours observed on breeding grounds is still not known. The repetition of aerial behaviour, such as breaches is energetically costly but can be observed frequently, sometimes over several hours (Whitehead 1985). One theory to explain the function of this behaviour is that breaches are used as an acoustic signal to other humpback males and females. It could be a spatial distance holder to other humpbacks - in similar way as singing is used (Tyack 1983). In the past it has been difficult to investigate the distance between breaching animals because most investigations are conducted from boats and therefore only one group of humpbacks can be observed at a time. The observation from the cliffs of the Isla de la Plata allow to obtain positions of sightings simultaneously and thus to calculate the distances between sightings. One of the theories why humpbacks migrate to tropical or subtropical waters to breed is that potential predators, such as orcas (Orcinus orca), are not as frequent. So far the only orca attacks on humpback whales in a breeding area have only been observed in Colombian waters (Flórez- González et al. 1994). Other cetaceans have been known to interact with humpback whales, but it is not always clear if these interactions are beneficial or detrimental to the humpbacks. Objectives of this chapter: Does the presence of calves and the observed behaviour of the whales indicate that the Machalilla National Park is used as a reproduction ground by humpback whales? Is breaching used as a spatial distance holder between humpback whale sightings? Do interactions between humpback whales and other cetacean species occur in the Machalilla National Park? 56

61 4.3 REPRODUCTIVE BEHAVIOUR Results Observed reproductive behaviour Some of the behaviour observed between humpback whales was agonistic in nature. On numerous occasions whales used a tail breach against another animal. Here, the rear third of the body was thrown out of the water and was slammed sideways and downwards against the water surface. Also fluke slaps and head lunges from one whale directed towards another whale were observed. Animals were seen to exhale underwater and creating bubbles, vocalising above the water ( trumpet blows ) and breaching as well as flipper slapping in close vicinity of other whales. Other behaviours associated with reproduction were belly flippering (in which an animal lies on its back while slapping with its flippers on the surface of the water), spyhops, rolling and headstands. On one occasion a humpback whale was observed to stay in the headstand position for up to 17 minutes before returning briefly to a lying position to breathe. A second whale was observed to stay under water apparently pushing its head against the ventral side of the headstand whale. This behaviour was observed continuously from shore continuously for 3 hours with the whale only returning to the vertical position to breathe. The sex of the animals could not be determined. Additionally humpback whales showed a variety of surface-active behaviours such as breaches as well as fluke and flipper slapping. The frequency of reproductive behaviour increased throughout the season. In the two-week period from June 23 rd to August 5 th, 67% of the sightings were engaged in reproductive behaviour (Figure 33). Towards the end of the season this percentage decreased again to 38%. % of groups showing reproductive behaviour to to to to to to 2.9. Figure 33. Increase in reproductive behaviour of humpback whales throughout the 1999 season. 57

62 4.3 REPRODUCTIVE BEHAVIOUR Group sizes A total of 109 sightings with a mean pod size of 2.33 (S.D.=1.05) were made from the vessels (254 whales). Pod sizes varied between one and a maximum of eight animals. The distribution of the pod sizes is shown in Figure 34. In the late season from the end of July to early August an apparent shift to larger mean group sizes (Figure 34) was not significant (χ²-test; p>0.05). The modal group size was 2 for all periods in the season. % of sightings th June to 8th July 9th July to 19th Aug 20th Aug to 18th Sep >6 group size Figure 34. Distribution of group sizes of humpback whales in early, main and late season Breaching as a spatial distance holder The distances between adjacent whale sightings during single scans were calculated using the data obtained from the observation point Escalera on the Isla de la Plata noted at the same time. As an example, the observer took the position of all humpback whale sightings at 10h00 and noted the behaviour of the whales. In the later analyses the distances between all sightings which included a breaching animal (during one scan) and the distances of sightings showing no form of surface display were calculated. Thus, if three sightings with a breaching animal each were seen during one scan a total of three distances for this category was obtained. A total of 32 separation distances were measured between sightings including one breaching animal. 49 distances were measured between sightings including no surface display, but instead were resting or travelling. All animals were within a 5-km radius of the Isla de la Plata. The mean separation distance between sightings that included breaching animals was significantly greater than that between sightings of resting or travelling animals, m (S.D.=3160.5) vs. 3642m 58

63 4.3 REPRODUCTIVE BEHAVIOUR (S.D.=2750.8) (U-test; p<0.05). Figure 35 and Figure 36 show the differences in the distribution of separation distances. 4 number of sightings distance between sightings (m) Figure 35. Distribution of distances between sightings including single humpback whales breaching. 7 6 number of sightings distance between sightings (m) Figure 36. Distribution of distances between sightings of groups of whales engaged in resting or travelling behaviour Mother-calf pairs On August 5 th 1999 we observed a calf that was estimated to be less than five meters long and that showed a dorsal fin that was doubled over, indicating a recent birth. The captain of the national park vessel observed the birth of a humpback whale calf in July 1995 close to the Isla de la Plata (pers. comment R. Gonzalez). In 1998 a humpback whale calf was caught by a fisherman close to the coast (at about W and S). We could not determine however if the calf was already dead when caught or died in the net. In the late summer of 2000 a calf about 5m long was found entangled in a net. The 59

64 4.3 REPRODUCTIVE BEHAVIOUR mother stayed close by. The calf was alive and was freed by a whale -watching crew (pers. comm. J. Morales). For pods with calves, a size of two signifies a mother-calf pair alone. Larger sized pods indicate that other whales were accompanying the mother-calf pair. It was more common for a mother-calf pair to be seen in the company of other whales than to be seen alone; 61.5% of all sightings consisted of three or more animals. There was never more than one calf in a pod percentage of sightings with calves mean group size percentage mean group size early season (10/6 to 8/7) mid season (9/7 to 19/8) late season (20/8 to 18/9) Figure 37. Seasonal changes in mean group size and percentage of sightings with calves in the 1999 season Of all sightings with calves 46.1% were triads of the mother, calf and an accompanying escort adult whale; making it the most common pod composition. 15.4% were part of a group of whales of more than 2 adults. 38.5% were mother-calf pairs. Throughout the season the group size of pods with calves increased. During the two-week period from 6 th to 19 th August all mother-calf pairs were accompanied by at least one other adult whale (Figure 37). 60

65 4.3 REPRODUCTIVE BEHAVIOUR Song Songs were heard throughout the season in all years ( ) using a hydrophone. We were not able to identify the singer or the direction from which the song came. Due to the difficulty of working on whale-watching vessels we could not conduct systematic acoustic surveys Interactions with orcas (Orcinus orca) A total number of 27 interviews was conducted with fishermen from Pto. Lopez (18), captains of tourist vessels going to the Isla de la Plata (3) and tourist guides that work the whole year in the Machalilla National Park (4). Combining the data available through interviews and our own sighting data from the years 1996 to 1999, we have gathered a total of 37 sightings of orcas from 1991 to The total number of orcas seen was 111. Information on the month of sighting was available for 36 sightings (110 animals). Most animals were seen in June, July, August and September (Figure 38). number of orcas Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 38. Number of orca sightings made from the years 1991 to 1999 in the different months 61

66 4.3 REPRODUCTIVE BEHAVIOUR Mean group size of orcas was 3 (S.D.=2.11) and modal group size was 2. The maximum group size was 10. A distribution of group sizes is shown in Figure % of sightings group size Figure 39. Distribution of group sizes for orca sightings. For 32 sightings the behaviour of the orcas could be determined (shown in Figure 40). In six cases (19%) we obtained accounts of orcas attacking humpback whales. All accounts are similar to the attack observed by myself (described below) in which several orcas were following one or more humpback whales, charging them and were the humpback whales were showing defensive behaviour such as fluke slashes towards the attackers. In five sightings (16%) orcas were following a group of humpback whales or were seen in their close vicinity. It is not clear whether the orcas were attacking or preparing for an attack. In 9 cases (27%) the orcas were feeding on fish; in one of these cases an adult male apparently stole the bait from a fishermen s net. For a total of 12 sightings (38%) orcas were seen travelling or porpoising (travelling fast enough to propel a large part of their body out of the water). 62

67 4.3 REPRODUCTIVE BEHAVIOUR feeding on fish 27% attacking humpbacks 19% following humpbacks 16% travelling 25% porpoising 13% Figure 40. Occurrence of different behaviours of orcas observed in the Machalilla National Park. In one case an attack of orcas on humpback whales could be observed in detail from a whale - watching vessel: Description of the attack observed August 9 th 1997 The vessel left Pto. Lopez at 9:25 heading for Isla de la Plata (bearing 320º). At 11:21 a group of two adult humpback whales with a calf (#1) was seen breaching at an estimated distance of 2000m. At 11:27 another group of two adult humpback whales (#2) was seen at a compass bearing of 000º and the same distance as sighting number one. At the time two other whale -watching vessels were with the group. Two adult male orcas were with group number one. At 11:30 we arrived at the sighting and maintained a distance of about 100m from the whales. Upon our arrival one of the other whale-watching vessels left. At this time all humpback whales (#1+#2) were together. The humpbacks displayed much surface activity, some of them lying on their sides and moving the lower part of their body rapidly through the water. Breaching stopped at this point and the animals began fluke and flipper slapping. All animals were very close together with the calf only visible at times in their middle. The orcas circled the humpbacks and were visible around the group of whales and twice within the group. At 11:45 the orcas left, travelling with a heading of 350º. The humpback whales remained close together and continued with their surface activity. At 12:02 another boat arrived. The humpback whales stayed close together and although they continued with their surface activity they began to travel with a bearing of 010º. At this time the calf fluked up and we observed that part of the fluke was missing. We left the sighting at 12:14. 63

68 4.3 REPRODUCTIVE BEHAVIOUR Interaction with false killer whales (Pseudorca crassidens) False killer whales were sighted several times in the study area. During one account the false killer whales could be observed together with humpback whales. T 4: 15:25 Humpbacks travelling fast Pseudorcas follow in a V-formation " # # ## ## ###### # # < Faro T 3: 15:15 Humpback "trumpet blow" %a " " # # # # # # # ## # < V # ## # # ### # # # # # ## # # # # # < T 2: 15:11 Humpbacks fluke up one group of Pseudorcas following the dive " " # # # ## # ## # ### # N # # V " # Humpback whales Pseudorcas T 1: 15:00 Humpbacks travelling fast; Pseudorcas following spread out in several groups Figure 41. Interaction between false killer whales (Pseudorca crassidens) and humpback whales observed from the Isla de la Plata on July 26 th The following is a description of the interaction, as seen from the island: 26 th July 1998 At 15:00 was the first sighting of false killer whales from the Bahia Drake on the Isla de la Plata and at 15:01 was the first sighting of this group from the observation point Faro, about 80m from the shore. The sighting consisted of several groups of four to six animals, with a total number of about 18 animals. Two mother calf pairs were identified in two different groups. The behaviour of all animals was directional fast swimming parallel to the coastline of the island. At 15:10 two adult humpback whales surfaced in the group of false killer whales. They were swimming close together, about 50m from the shore in the same direction as the false killer whales. One group of false killer whales was in front of the humpbacks and one animal was seen swimming in the bow of one of the humpbacks. The other groups followed, spread out. Both humpbacks fluked up and the group in front followed them down, while the others stayed in their spread out groups and continued swimming. When the humpbacks came up to breathe one of them vocalised above water (trumpet blow). They continue swimming fast and parallel to the shoreline. The false killer whales changed into a V-formation following the humpbacks, now all behind them. The sighting ended at 15:25 because the animals were out of the field of vision. 64

69 4.3 REPRODUCTIVE BEHAVIOUR Interaction with Dolphins Dolphin groups of up to 400 animals were seen around the island. They were not resident and the species, when identified, were bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris) and pan-tropical spotted dolphins (Stenella attenuata). Although at times dolphins and humpback whales occurred in the same general area around the island, they normally did not seem to interact with each other. One exception is shown in Figure 42 where a pod of two adult humpback whales was intercepted by a group of about 50 pan-tropical spotted dolphins. The dolphins seemed were feeding but interrupted their activity to approach the humpbacks. They surrounded them and were seen to ride in front of the animals in the bow-wave. One of the humpbacks started to vocalise above water (trumpet blow). Both humpback whales travelled the whole time :29 16: : humpback whales 15:31 dolphin group 16: Figure 42. Observed interaction between a group of spotted dolphins and two humpback whales as recorded with the theodolite from the Isla de la Plata. 65

70 4.3 REPRODUCTIVE BEHAVIOUR Discussion Behaviour, pod size and pod composition Mobley and Herman (1985) found in Hawaiian waters that 64% of the pods that contained calves consisted of 3 or more animals. The Machalilla National Park has a similar percentage of sightings in which mother-calf pairs are accompanied by one or more adult whales. At the beginning of August the group size of sightings with calves increased to a modal group size of three. The escorts of mother-calf pairs are thought to be males seeking access to reproductively-active females (Clapham et al. 1992; Tyack 1981). Although the probability of post-partum ovulation leading to successful conception is not high, escorting a female with calf may be a male reproductive strategy that has some success (Corkeron et al. 1994; Glockner-Ferrari and Ferrari 1985). The mean pod size of humpback whale sightings increased from the end of July to the beginning of September. Such an increase can be explained in part by the presence of calves, but also by the formation of competitive groups. Competitive groups were first described in detail by Tyack and Whitehead (1983) as well as by Baker and Herman (1984), who suggested that such groups consist of several adult males competing for sexual access to a single mature female. Certain behaviours which are associated with reproduction occur particularly often within a competitive group. Because several males vy for access to single females (Baker and Herman 1984, Clapham et al. 1992; Tyack and Whitehead 1983) a variety of agonistic behaviours can be observed. Winn and Reichley (1985) describe head lunges used between male humpback whales in competitive groups. The scar patterns on fin and body demonstrate the violent interactions between male humpbacks (Baker and Herman 1984; Chu and Nieukirk 1988). Additionally, bleeding has been observed (Clapham 1996) and one death following an aggressive interaction has been recorded (Pack et al. 1998). Behaviour associated with breeding Any position in which an animal lies on its back (e.g. belly-flippering) is thought to be a behaviour in which a female denies access to one or several males. Although this behaviour is non-aggressive it effectively prevents males mating. The prolonged head-stand behaviour observed in this study might have been executed in a similar context. Unfortunately, it is extremely difficult to determine the sex of an individual humpback in the field and therefore one cannot be sure if the head-stand behaviour observed is the case of a female trying to avoid a male. Song and aerial behaviour as a spacing mechanism Communication is not only an exchange of information but it can also reflect an attempt by a signaller to manipulate the behaviour of a recipient (Krebs and Dawkins 1986). One of the most famous displays of information is the humpback whale song (Payne and McVay 1971; Winn and Winn 1978). Humpback whale songs are a distinctive continuous sequence of vocalisations generally performed by males (Whitehead 1985). Singing is almost never heard at the feeding grounds (Perkins and Whitehead 1977) and research by Tyack (1981) off Hawaii relates singing to 66

71 4.3 REPRODUCTIVE BEHAVIOUR mating. Song appears to function as a spacing mechanism between male humpbacks (Frankel et al. 1995; Helweg et al. 1992; Tyack 1981). Tyack (1999) concludes that humpback whale song is used in intra- and intersexual selection at the same time. The fact that we were able to listen to songs in the Machalilla National Park provides further evidence that the study area is used as a breeding area. Tyack (1983) noted an average distance of 6km between singers off Maui and suggested that song may function to maintain that spacing. Frankel et al. (1995) used visual and acoustic methods to investigate the spatial distribution of singing humpback whales. They found that the separation distance between singers (mean 5.1km) was significantly greater than that between non-singing singletons (mean 2.1 km). They also found a correlation between breaching and the cessation of singing which suggests that the sounds of aerial behaviour can also convey information to other whales. Aerial behaviours are known to produce sound in humpbacks and other species (Clark 1983; Whitehead 1985). Various authors (e.g. Clark 1983; Herman and Tavolga 1980; Norris et al. 1983) consider that the loud splash made when breaching, flipper, or fluke slapping may have an important signalling role, presumably between males which might display their strength or may breach as a challenge to other males when in competition for females. Whitehead (1985) states that breaches, flipper and fluke slaps make a loud sound both above and below the surface where they can be heard with a hydrophone. He also describes that breaching is generally louder than fluke slapping, which is louder than flipper slapping. However, the acoustic output of a breach probably depends as much on style as on power. Although the energetic cost is high compared to song, the sound of an aerial behaviour such as a breach may indicate the breaching animal s location and perhaps its behavioural state. The separation data show that the mean distance between sightings including breaching animals is larger than the distance between resting or travelling animals. While singers are almost certainly all males (Glockner-Ferrari and Ferrari 1990; Lambertsen et al. 1988), the identity of breaching animals is not known, although Whitehead (1985) suggests also that they are males. Aerial behaviours may allow females to locate displaying males. The message is to both sexes, for the females to convey location and an indication of reproductive fitness, breaching frequency and duration is related to physical fitness and thus may be equally important to a female than the message given through song. Whitehead (1985) showed that although a single breach is not significant in the daily energy budget of a humpback whale, it is an indicator of the musculature and power of an animal. If a breach is a reliable indicator of strength, a series of breaches may be an index of the stamina of a humpback in aggressive or courtship display. Not only will the opponent measure the fitness of his competitor, but the female may also derive fitness of the male. The intrasexual message is to maintain the spacing between breaching animals. Males can hear the breaches and can interact with the other whales, possibly in an attempt to displace them. 67

72 4.3 REPRODUCTIVE BEHAVIOUR Interspecific interactions The interactions with dolphins seem to be mostly of advantage to the dolphins. They seem to enjoy bow-riding and the fact that the humpbacks vocalised above water might indicate that they did not benefit from this interaction as much as the dolphins. False killer whales, however, are known to attack small cetaceans and might pose a threat to humpback whales as well (Perryman and Foster 1980). Nevertheless, the observed interaction between the humpback whales and the false killer whales probably was a case of molesting and not an attack with the intention of killing. Although both false killer whales and dolphins might have a nuisance value for the humpbacks, they do not seem have any major effect. Orcas are known to attack other cetaceans, including the largest rorqual, the blue whale. In tropical breeding grounds orca attacks on humpbacks have so far only been observed at the Colombian breeding ground (Florez-González et al. 1994). Judging from the observations made during this study and the conducted interviews, it seems that orcas commonly attack humpbacks in the Machalilla National Park during their breeding season. The type of attack in which the humpbacks keep the calf in their middle and move their flukes vertically or slash them from side to side seems similar to that observed in other mysticete and odontocete species (Caldwell and Caldwell 1966; Whitehead and Glass 1985). Clapham (2000) believes that orcas are mostly attacking humpback whale calves which might explain the high percentage of mother-calf pairs which were accompanied by another humpback whale (61.5%). The higher number of accompanying adult whales could thus increase a successful protection of calves from predators. So far in Ecuadorian waters, there has been no report of the death of a humpback due to an orca attack and it is doubtful that humpbacks are a substantial part of the diet of these predators. The high number of observations in which the orcas were seen feeding on fish seems to indicate that humpbacks might be potential prey but not a major focus. Conclusions: The humpback whales in the Machalilla National Park show a wide array of reproductive behaviour and in the late season (20 th August to 18 th September) almost 18% of all sightings include a calf. This confirms that the area is used as a breeding ground for humpbacks. Breaching is used as a spatial distance holder between humpback whales. Orcas have been observed to attack humpback whales in the Machalilla National Park. 68

73 4.4 INTERACTION WITH WHALE-WATCHING VESSELS 4.4. INTERACTION WITH WHALE-WATCHING VESSELS 69

74 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Introduction Whale-watching operations are already well established in several parts of the world, particularly in the USA. In the Machalilla National Park the first observations of humpback whales were conducted by researchers in the late 1980s. Only in the last five years has whale -watching been commercialised and interest in humpbacks as a tourist attraction has increased dramatically. An ongoing concern has been that, if not pursued appropriately, whale-watching will result in an unacceptable and harmful level of disturbance to the whales. It has been recognised that harassment could have both short-term and long-term effects for humpback whales (Norris and Reeves 1978). Short-term effects would include display of behaviours such as avoidance and aggression towards a vessel. Long-term effects of harassment on critical behaviours such as feeding, resting and mating reduce the biological fitness of the population. From what is known so far, reactions of humpbacks to vessels vary considerably with some animals showing little or no reaction when vessels are close. For example, Watkins et al. (1981) reported that passage of a tanker within 800m did not disrupt feeding in humpbacks. They generally seem less likely to react when actively feeding compared to resting or when engaged in other activities (Krieger and Wing 1984, 1986). In contrast, in a study of the effects of vessel noise on humpback whales summering in Alaska, Baker and Herman (1989) demonstrated a number of significant responses including decreases in breathing intervals, increases in dive durations and orientation away from the path of moving boats, often at ranges of up to 3-4km. Successful reproduction of humpback whales is especially important and if, due to disturbance, breeding success is reduced or if mortality of the calves increases, the survival and recovery of the population are in danger. While in their breeding grounds humpback whales live off their blubber reserves obtained during the feeding season and are therefore more susceptible to additional stress. Young calves are especially dependent on sufficient time with their mothers to suckle and rest. For them any disruption will lead to a reduced fitness. In practical terms it is feasible to measure short-term changes in behaviour which correlate with potential sources of disturbance. When trying to determine the effects of whale -watching boats on the behaviour of humpbacks, it is important to control for the effects due to individuals and to location. This emphasises the importance of being able to observe the same whales before, after and during encounters with whale-watching vessels. However such data have been difficult to collect because most studies have been made from vessels which means that one can never be sure if the observer himself has an effect on the behaviour of the whales and the pre -vessel phase cannot be observed. 70

75 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Due to its unique location, the Isla de la Plata is an ideal observation point for interactions between humpback whales and whale-watching operators without influencing the animals behaviour. Also the observations provide paired data in which the same whales can be observed before, during and after an interaction. Objectives of this chapter: How is whale-watching in the Machalilla National Park carried out and what are the potential conflicts occurring with humpback whales? Do humpback whales change their speed, course or behaviour when followed by whale-watching vessels? Are changes related to group sizes or presence of calves? Can we observe agonistic behaviour of humpbacks toward whale -watching vessels? 71

76 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Results Trackings of humpbacks and whale-watching vessels In 1998 and 1999 a total of 73 trackings were made which included interactions between whalewatching vessels and humpback whales. In 27 trackings whales could be observed either before the interaction and during the interaction, or during the interaction and after the interaction. Observation for the categories before, during or after were at least 20 minutes long. These were analysed for changes in speed and course (see ). The maximum number of vessels with a group of whales was eight vessels, the maximum time a single vessel spent with the whales 2 hours and 44 minutes. The maximum time a group of humpbacks was with one or more whale-watching vessel was 4 hours and 49 minutes. In the following figures some typical trackings of humpback whales and the descriptions of the interactions with commercial whale-watching vessels are documented. The projection used for the figures is UTM (Universal Transversal Mercator); an increase of one on the x or y axis equals one meter in distance. The vessels generally leave Pto. Lopez in the morning between 8h00 and 10h00 and arrive in the waters around the island one to two hours later. The tourists spend several hours on the island and most vessels leave again between 14h00 and 16h00 to return to the mainland. Whenever sightings of humpbacks are made the vessels stop to observe. The first trackings (#1 to #4) show typical interactions of humpback whales with one or two whale - watching vessels. Either the whales were seen first with the vessel and then observed after the vessel had left, or they were seen first without the vessel and followed during the interaction. In one case (#4) one whale was observed before, during and after a very short interaction with a whale-watching vessel. Trackings #5 to #7 show examples of the situation when one vessel started the observation and a second vessel continued to observe the same sighting once the first vessel had left. Thus one group of humpback whales was continuously with at least one vessel although individual vessels might not have stayed longer than half an hour. The trackings #8 to #11 show the situation of several vessels arriving at the same time and all staying to observe the same group of whales. Up to 7 vessels have been seen around one group and up to 12 vessels in an area of 5x5km at the same time. This situation is brought on because the vessels communicate via radio to inform each other of sightings and also because most boats arrive at the Isla de la Plata at around the same time. 72

77 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Trackings with one or two whale-watching vessels: Tracking #1: :05 13:42 13:12 13: :01 12: :41 12:27 whales vessel 14: Figure 43. Tracking #1 on the A group of three adult humpback whales was first sighted at 11:51 when the animals were milling. The whale-watching vessel started with the observation at 12:43. The humpbacks showed logging and resting behaviour until 13:04 when they started to travel slowly, although not in any consistent direction (milling). This continued until the vessel left at 13:35. The humpbacks continued to travel slowly in a generally southerly direction and their last position was taken at 14:58. Tracking #2: :37 11:17 whales vessel :55 10:35 11:10 11:16 10:48 10: : Figure 44. Tracking #2 on the A group of two adult whales were seen travelling and breaching when they were first sighted at 10:35. The vessel stayed with the humpback whales for 32 minutes until 11:07. When the vessel left the behaviour of the group changed to slow travelling. 73

78 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Tracking #3: whales vessel 1 vessel :48 10:44 11:48 11:38 11: Figure 45. Tracking #3 on the A group of five humpback whales, including one calf, was first sighted at 9:48 when they were seen resting. At 11:03 whale-watching vessel 1 was with the sighting and at 11:06 whale-watching vessel 2 joined. They both left at 11:48. The humpback whales were travelling slowly and engaged in flipper slapping while they were with the vessels. Tracking #4: whale :19 vessel : : : : Figure 46. Tracking #4 on the The single adult humpback was first seen at 14:04 travelling in no clear direction (milling). At 15:23 the whales were observed by the whale-watching vessel until 15:33. The whale continued exhibiting the same behaviour throughout the tracking. 74

79 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Trackings in which the same sighting is observed by different vessels continuously: Tracking #5: whales vessel 1 vessel 2 10:14 10: :39 10:52 10: :54 11: Figure 47. Tracking #5 on the of a group of 5 whales, one of them a calf. The group was first seen at 10:14 when they were already with whale-watching vessel #1. Some of the animals were showing surface active behaviour such as flipper slaps and head slams. At 10:31 they travelled slowly without any surface display. At 11:36 some animals started again with head slams and fluke slaps. At 12:06 the humpbacks started milling until 12:30 when they started to travel and were lost to the observers. The whale-watching vessel #1 stayed at total of 38 minutes with the humpbacks until it left at 10:52. Whale-watching vessel #2 was first sighted at 10:21 and was with the whales at 10:24. It followed the group for 1 hour and 24 minutes, until it left at 11:48. 75

80 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Tracking #6: :05 whales :24 vessel 1 vessel :32 15:32 15:19 15: :42 15: :51 16: Figure 48. Tracking #6 on Three adult humpback whales were first sighted at 15:08 when they were socialising and milling. At 15:19 they were joined by the first whale-watching vessel which stayed until 15:40. At 15:33 a second whale-watching vessel had joined the sighting and continued to observe until 16:00. After the second vessel left the animals started to travel very slowly and showed resting behaviour. Tracking #7: :40 11:44 10: :29 13:26 11: :13 whales vessel 1 vessel Figure 49. Tracking #7 on the A group of two adult whales was observed twice by two different whale-watching vessels. The first vessel arrived at the sighting at 11:18 and stayed with the animals until 11:42. The second vessel arrived at 12:54 and stayed with the group until 13:18. The humpbacks showed milling and resting behaviour until about 13:28 when they started to travel. 76

81 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Trackings with several whale-watching vessels: Tracking #8: :49 9: :52 11: : : whales 11:38 10: vessel vessel vessel 3 12: Figure 50. Tracking #8 on the A group of seven humpback whales including one calf was first sighted at 9:44. Their behaviour was milling. The first whale-watching vessel arrived at the sighting at 10:28. It left again at 10:48. Whale-watching vessel 2 was with the sighting at 10:33 and left again at 10:50. While the whale-watching vessels was with the group the animals changed their behaviour to travelling. At 10:49 whale-watching vessel 3 approached the whales and stayed until 11:02. The whales continued travelling in a southern direction after all vessels had gone. Tracking #9: whale vessel 1 vessel : :29 9:49 10:31 10:19 10: :09 8:50 11:05 10:25 10:37 10:58 11:

82 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Figure 51. Tracking #9 from One single adult humpback whale was first sighted at 8:50. The behaviour was travelling, including flipperslapping and headslams. The whale-watching vessel 1 arrived at 10:25 at the sighting, whale-watching vessel 2 arrived at 10:31. Both left the whale again at 11:03. Throughout the interaction the whale continued with flipperslapping and headslams while travelling. Tracking #10: :41 9: :38 whales :43 vessel 1 vessel :13 10:22 vessel 3 vessel :05 vessel Figure 52. Tracking #10 on The group consisted of three adult humpback whales. A total of five whale-watching vessels was with the sighting from about 10:42 to 11:10. The humpbacks were initially milling with a lot of surface behaviour and no defined direction. During the interaction with the vessels the animals changed their behaviour to travelling but continuing with surface behaviour. 78

83 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Tracking #11: :47 11:11 11:44 11:36 11:20 11: whales vessel vessel : Figure 53. Tracking #11 on Track of six adult humpback whales which were travelling and flipperslapping when first sighted with two whale-watching vessels at 11:20. When the vessels left at 11:38 and 11:45 the humpback whales started to travel without any surface behaviours. 79

84 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Changes in speed and course In 12 cases the whales could be observed before a whale -watching vessel arrived and during the following observation. All sightings were made for a minimum of 20 minutes for each category ( before and during ) and a minimum of five positions for the sighting in each category. Two factors, speed and course, were chosen to determine whether the presence of vessels had an effect on humpbacks. Speed of humpback whales increased significantly during the interaction with the vessel (Wilcoxon-test for paired data; p<0.02) while the course did not change significantly (p>0.5) (Figure 54 and Figure 55). mean speed (km/h) before observation during observation sighting number Figure 54. Changes in speed of humpback whales before and during an interaction with a whale-watching vessel. The increase in speed was significant (Wilcoxon-test; p<0.02). 5 4 before observation during observation course sighting number Figure 55. Changes in course of humpback whales before and during an interaction with a whale-watching vessel. No significant difference was observed (Wilcoxon-test; p>0.5). 80

85 4.4 INTERACTION WITH WHALE-WATCHING VESSELS In another 15 cases the humpback whales were observed with a vessel ( during ) as well as after the vessel left. Each category ( during and after ) was observed for a minimum of 20 minutes and a minimum of five positions in each category. Again changes in speed and course were used to determine whether humpbacks showed different behaviour in the presence of whale-watching vessels. Speed and course did not change significantly when comparing during and after categories (Wilcoxon-test for paired data; p>0.5 for speed and course). mean speed (km/h) during observation after observation sighting number Figure 56. Changes in course of humpback whales during and after an interaction with a whale-watching vessel. No significant difference could be seen (Wilcoxon-test; p>0.5). course 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 during observation after observation sighting number Figure 57. Changes in speed of humpback whales seen during and after an interaction with a whale-watching vessel. No significant difference could be seen (Wilcoxon-test; p>0.5). 81

86 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Calves Differences due to group size or composition To determine whether humpback whale sightings reacted differently according to presence of calves the 27 trackings were combined to categories "with vessel" and "without vessel". The "without vessel" included the categories of before and after an interaction. 12 trackings were made up of sightings including a calf, 15 groups tracked did not include a calf. A decrease in course value indicates that the animals swam in a straighter line, whereas an increase indicated that the animals swam in a course with deviations. Behaviour changes were considered definite changes from one behavioural category to the next, e.g. from resting to travelling. Groups with calves showed no significant differences in speed (p=0.89), behaviour changes (p=0.91) and course (p=0.89) (Fisher-test) when compared to groups without calves. percentage trackings with calves lower speed during interaction higher speed during interaction trackings without calves all trackings Figure 58. Changes in speed for trackings with calves, without calves and all trackings combined. Speed did not change significantly between sightings including a calf and sightings without a calf (Fisher-test; p=0.89). percentage trackings with calves no change in behaviour during interaction change in behaviour during interaction trackings without calves all trackings Figure 59. Changes in behaviours for trackings with calves, without calves and all trackings combined. Behaviours did not change significantly between sightings including a calf and sightings without a calf (Fisher-test; p=0.91). 82

87 4.4 INTERACTION WITH WHALE-WATCHING VESSELS percentage trackings with calves straighter course during interaction less straighter course during interaction trackings without calves all trackings Figure 60. Changes in course for trackings with, without calves and all trackings combined. A straighter course is indicated by low values, a less straight (more deviating) course by higher values. Course did not change significantly between sightings including a calf and sightings without a calf (Fisher-test; p=0.89). Group size To determine whether humpback whale sightings reacted differently according to group size the 27 trackings were again combined to categories "with vessel" and "without vessel. The trackings were put into two categories, 1 or 2 animals (11 trackings) and 3 or more animals (16 trackings). There was no significant difference in course (p=0.65) or behaviour (p=0.52) between groups. There was, however, a significant difference in speed (p<0.05) between the two different group sizes, with the larger groups reacting to the presence of whale -watching vessels with an increase in speed. decrease in speed increase in speed percentage or 2 3 or more Figure 61. Change of speed according to different group sizes. The larger groups reacted significantly different to the presence of whale-watching vessel compared to the smaller groups (Fisher-test; p<0.05). 83

88 4.4 INTERACTION WITH WHALE-WATCHING VESSELS no change in behaviour change in behaviour percentage or 2 3 or more Figure 62. Change of behaviour according to group size. The different group sizes did not react different to the presence of whale-watching vessel (Fisher-test; p=0.52). decrease in course increase in course percentage or 2 3 or more Figure 63. Change of course according to group size. The different group sizes did not react different to the presence of whale-watching vessel (Fisher-test; p=0.65). 84

89 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Change of speed: a case study On the 28 th of August 1998 a group of four adult humpback whales was followed from 10:14 to 12:44. The group was followed by two whale-watching vessels when it was first sighted. The behaviour of the group varied between travelling and social interactions. At 10:18 a head-slam was observed, at 11:29 and at 11:37 fluke slaps were observed (arrows in Figure 64). After the vessels left no more agonistic behaviour could be observed. In Figure 64 we can see the mean speed for each five minutes of observation. The blue columns show the speed when two whale -watching vessels were with the humpbacks. The vessels left at 11:45 (white columns) and the speed of the whales dropped. The mean speed for the observation period with the vessels was 2.04 km/h and for the observation period without the vessels 0.64 km/h (χ²-test; p<0.0001). 20 mean speed (km/h :15 10:25 10:35 10:45 10:55 11:05 11:15 11:25 11:35 11:45 11:55 12:05 12:15 12:25 12:35 12:45 Figure 64. Example of the changes in mean speed of a group of humpback whales while with a whale-watching vessel. Red arrows indicate when whales displayed agonistic behaviour. 85

90 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Discussion It is very difficult to determine the influence of whale-watching vessels on cetaceans. First of all, whales can show different reactions to human presence. If animals approach a boat or humans this is considered a positive reaction. It is also possible that the whale does not react at all, or shows a negative reaction. Reactions can be visible to a human observer, such as a change in behaviour or swimming speed. But long before the whales show such an obvious response, they are likely to react at a physiological level, for example, hormonally. Therefore, to investigate reactions of whales humans have to rely on reactions which are noticeable and measurable, these often being cross measures of potentially complex physiological changes. Changes in speed When observing whales in the field it can be difficult to judge a change in speed correctly. The observations with the theodolite gave ideal conditions to analyse the occasions when the same group of whales were observed before, and/or after encounters with whale -watching boats. The observed increase in speed when comparing the "undisturbed time" before the interaction with the time of the encounter is significant. For the during and after case, however, no significant decrease of speed was observed, although this might be expected. Green and Green (1990) were able to look at changes in speed and they found that humpbacks reduced speeds after the boat departed. In the case of the Machalilla humpback whales it might that this decrease could not be observed because some animals where increasing their speed to actively avoid the vessel in the during time and that this behaviour continued after the vessel had left. Changes in behaviour A systematic study of short-term reactions of Hawaiian humpbacks to vessels was done by Bauer (1986) and Bauer and Herman (1986). Results differed among categories of whales, depending whether the sighting consisted of singers, other singletons, mothers or calves. Overall, humpbacks attempted to avoid vessels and sometimes directed threats toward them. Obvious agonistic behaviour towards whale-watching vessels were rare in this study, but it did happen in several cases. The behaviours used, such as charging or tail slapping, can also be seen in agonistic interactions between the whales. This change in behaviour would probably not lead to a dramatic increase in energetic expenditure of the whale, but will take time from the whales' normal behaviours. Presence of calves and group size Bauer et al. (1993) found that smaller pods and pods containing a calf were more affected by the presence of vessels than were larger pods. In contrast, in the Machalilla National Park, a significant difference could only be observed in relation to larger groups which increased their speed more often than smaller groups. The lack of differences seen in sightings with calves is probably due to the small sample number. The number of trackings was not sufficient to conduct a detailed analyses of group composition and the presence of calves. 86

91 4.4 INTERACTION WITH WHALE-WATCHING VESSELS Influence at a population level Humpback whales return annually to their feeding and breeding grounds. Even the whaling activities which repeatedly killed animals in the same areas were not able to disrupt this very conservative behaviour. On the one hand, this strong site fidelity indicates that animals are fairly tolerant to human disturbance and will probably not change their habitat due to vessel presence. On the other hand, this site fidelity indicates that the areas are extremely important to the biology of the humpbacks because they do not give them up. The data on long-term changes in behaviour or habitat-use by humpback whales are contradictory. Around the summer feeding grounds off Cape Cod humpbacks remain for extended periods and return annually, despite exposure to many ships, fishing vessels, and whale-watching boats (Beach and Weinrich 1989; Clapham et al. 1993). There is some indication that humpbacks do change habitat use. Humpback whale density may be inversely related to the daily amount of boat traffic and to the local amount of human activity (Herman 1979). The Hawaiian population seems to be increasing despite exposure to human activities, so long-term negative effects are not apparent at the population level (Bauer et al. 1993). Some longer-term Hawaiian studies suggest that mother calf pairs become proportionally less frequent close to shore when recreational boating increases (Glockner-Ferrari and Ferrari 1985, 1990; Salden 1988). Calves would seem to be especially susceptible to vessel traffic because they might have fewer chances to suckle if the mother is forced to increase her speed or to change her behaviour from resting to travelling. One of the problems in studying whales is that their behaviour is influenced by individual differences which we cannot observe. Some whales seem to be more tolerant of whale -watching boats and quite often these individuals are the ones to which most whale-watching effort is directed. Such whales could be inherently more tolerant of boats or could have become habituated to them over time. To detect behavioural reactions which can be used in a generalised way, larger sample sizes are needed. Nevertheless the fact that in the Machalilla humpback whales increase their speed when whale-watching vessels arrive, is most likely to be of biological significance. These whales do not feed and use their fat reserves for the high energetic demands - the females to calve and subsequently to lactate, while the males engage in active reproductive displays. To what extend such short-term behavioural changes affect the fitness of individuals in the longer-term is extremely difficult to measure. Continuing monitoring is advisable in order to investigate any longterm effects of human disturbance. Conclusion: Humpback whales significantly increase their speed when observed by whale-watching vessels. In some cases agonistic behaviour from humpback whales towards whale-watching vessels could be observed. Further investigations are needed to determine in what way the presence of calves and/or group size influence reactions of whales. 87

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93 4.5 MANAGEMENT AND CONSERVATION 4.5. MANAGEMENT AND CONSERVATION OF HUMPBACK WHALES 89