Short Note. Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia

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1 Aquatic Mammals 2013, 39(4), , DOI /AM Short Note Behavioral Observations of Coastal Irrawaddy Dolphins (Orcaella brevirostris) in Trat Province, Eastern Gulf of Thailand Louisa S. Ponnampalam, 1 Ellen M. Hines, 2 Somchai Monanunsap, 3 Anoukchika D. Ilangakoon, 4 Chalatip Junchompoo, 5 Kanjana Adulyanukosol, 6 and Laura J. Morse 7 1 Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia louisa.ponnampalam@gmail.com 2 Department of Geography and Environment, Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA 94920, USA 3 Southern Marine and Coastal Resources Research Center, Department of Marine and Coastal Resources, Songkhla 90100, Thailand Grandburg Place, Maharagama, Sri Lanka 5 Eastern Marine and Coastal Resources Research Center, Department of Marine and Coastal Resources, Rayong 21170, Thailand 6 Marine and Coastal Resources Research Center, Upper Gulf, Department of Marine and Coastal Resources, Samut Sakhon 74000, Thailand 7 Office of Protected Resources, National Marine Fisheries Service, Silver Spring, MD 20910, USA The Irrawaddy dolphin (Orcaella brevirostris) is found in Southeast Asia in nearshore coastal, estuarine habitats, in three freshwater riverine habitats of the Mahakam, Mekong, and Ayeyarwady Rivers, and in brackish water lakes in Chilika, India, and Songkhla, Thailand (Reeves et al., 2008). Throughout its range, the Irrawaddy dolphin has been studied primarily in riverine and brackish habitats such as the Mekong (Stacey & Hvenegaard, 2002; Baird & Beasley, 2005), Ayeyarwady (Smith & Mya, 2007) and Mahakam Rivers (Kreb, 2004a; Kreb & Budiono, 2005); the Chilika Lagoon (Sutaria & Marsh, 2011); the Songkhla Lake (Beasley et al., 2002); and the Malampaya Sound (Dolar et al., 2002; Smith et al., 2004). Coastal populations have been studied to a lesser extent, mainly in areas such as Australia (Parra et al., 2006, 2011), Bangladesh (Smith et al., 2006), Malaysian Borneo (Minton et al., 2011, 2013), and eastern Thailand (Hines et al., 2008, 2009, 2012, 2013). Most research efforts have been focused on estimating population sizes for conservation efforts as this species is listed as Vulnerable on the International Union for Conservation of Nature s (IUCN) Red List of Threatened Species and thought to be undergoing decline (Reeves et al., 2008); however, certain subpopulations such as the ones in the Songkhla Lake (Smith & Beasley, 2004) and the Mekong River are listed as Critically Endangered (Smith & Beasley, 2004; Beasley et al., 2013). Very few detailed behavioral studies on this species are available in the literature on the whole (Stacey & Hvenegaard, 2002; Kreb, 2004b; Kreb & Rahadi, 2004; Beasley, 2007; Parra et al., 2011) or are unpublished, leaving much to be explored. In this short note, we describe Irrawaddy dolphin behaviors that were observed during boat and aerial surveys in the eastern Gulf of Thailand. Documented behaviors included probable foraging for cephalopods (as suggested by squid ink and loose tentacles floating at the surface), and herding and tactile social actions with animals layered vertically in the water column, suggesting mating in large aggregations (Table 1). Trat Province in the eastern Gulf of Thailand is the easternmost province of Thailand, approximately 315 km east of Bangkok, with an open stretch of coastline extending to the Cambodian border. The area consists of a very shallow bay (< 5 m depth) to the northwest and several estuaries along the southeastoriented coast (Figure 1). The coast has a gently sloping shallow bathymetry with an average depth of 7 m within 3 km of shore. It was chosen as the site for our research on Irrawaddy dolphins after aerial surveys in 2003 to 2005 for dugongs (Dugong dugon) conducted by Hines et al. (2003, 2004, 2005) yielded numerous incidental sightings of these dolphins, including herding behavior during a dugong survey in At that time, coastal Irrawaddy dolphins had not previously been studied in this area. We made behavioral observations of Irrawaddy dolphins off the coast of Trat Province from aerial surveys in 2004, 2008, and 2009, and from boat-based line transect surveys conducted

2 402 Ponnampalam et al. Table 1. The dates and locations of observed feeding associated with cephalopods, herding, and pair mating for Irrawaddy dolphins off the coast of Trat Province, Thailand, Date (d/mo/y) Behavior observed Latitude (h.dddddd ºN) Longitude (h.dddddd ºE) 9/1/2004 Herding /1/2004 Herding /2/2008 Herding /2/2008 Probable feeding and squid ink /3/2008 Herding /1/2009 Probable feeding and squid ink /1/2009 Probable feeding and squid ink /1/2009 Probable feeding and squid ink /1/2009 Probable feeding and squid ink /1/2009 Probable feeding and squid ink /1/2009 Probable feeding and squid ink /1/2009 Herding /3/2009 Probable feeding and squid ink /3/2009 Probable feeding and squid ink /3/2009 Pair mating /1/2012 Probable feeding and squid ink /1/2012 Herding /1/2012 Herding /1/2012 Herding /1/2012 Herding /1/2012 Probable feeding and squid ink /1/2012 Probable feeding and squid ink /2/2013 Herding /2/2013 Herding /2/2013 Herding Group size in 2008, 2009, 2012, and 2013 (Figure 1) (Hines et al., 2008, 2009, 2012, 2013). All surveys were conducted in January and February during the northeast monsoon season (October-March). Aerial surveys were conducted in an ultralight fixed-wing aircraft along the shoreline with opportunistic observations made by a single observer at an average altitude of 225 m. Photographs were taken using a Nikon D40X D-SLR camera with a 75 to 300 mm zoom lens. Boatbased surveys were conducted from a 10.5 m fishing vessel with a viewing deck height of 6 m above sea level and with three dedicated observers on effort during line transect sampling. All Irrawaddy dolphin groups observed during boat surveys were photographed using a Canon EOS40D D-SLR with a 100 to 400 mm zoom lens. A description of the various behaviors observed follows. Foraging for Cephalopods During boat-based surveys in 2008, 2009, and 2012, we observed squid ink in the vicinity of Irrawaddy dolphin groups (within 3 to 5 m) on 12 different occasions (Table 1). On one of these occasions, squid tentacles were seen floating near the surface of the water. The mean group size during these sightings was 7.2 individual dolphins (SD ± 4.2, n = 12, range = 2 to 18). On two separate occasions during aerial surveys in March 2009, Irrawaddy dolphins in groups of at least four to seven individuals were sighted encircling prey just under the surface of the water. Within a minute of our observation of the Irrawaddy dolphins circling behavior, dark clouds of squid ink appeared on the surface of the water; several individual dolphins in the group were assumed to be feeding from within the cloud of ink (Figure 2). The groups dispersed after approximately 2 min, and our observations ceased. In both observations, the groups spacing remained tight (i.e., individuals were not more than 2 m apart from each other). Pair Mating We observed pair mating behavior once during an aerial survey in March 2009 near the town of Khlong Yai near the Cambodian border (Figure 1). Two Irrawaddy dolphins were seen pursuing each other for approximately 2 min. One individual was swimming belly-up while the other was swimming towards it (as described in Saayman et al., 1973) before both individuals aligned their bodies belly-to-belly to copulate (Figure 3). The copulation lasted 40 s, and the pair separated and swam away in opposite directions (Figure 3). Herding During both our aerial and boat surveys, we observed large groups of adult and/or subadult Irrawaddy dolphins engaging in intense social behavior that appeared to be herding with probable mating.

3 Trat Irrawaddy Dolphins 403 Figure 1. The location of Trat Province, eastern Gulf of Thailand, including the boat-based line transect survey design and sighting locations of probable feeding associated with presence of squid ink, pair mating, and herding behaviors observed during aerial and boat-based surveys in 2008 through 2013

4 404 Ponnampalam et al. Figure 2. Irrawaddy dolphins feeding on cephalopods in squid ink Throughout these activities, which lasted approximately 20 to 60 min, there appeared to be one animal in the center of the group that the other dolphins were attempting to access; the center animal would appear to try to swim away from the group only to be blocked by the individuals surrounding it. These animals were seen swimming belly-to-belly and intertwining with each other, behavior that was indicative of copulation attempts. Once these intense social bouts subsided, the Irrawaddy dolphins dispersed into smaller subgroups and became difficult to track and re-approach: they submerged for longer durations (up to 5 min) and surfaced unpredictably. These episodes were observed during an aerial survey in January 2004 (for dugongs) (n = 2) and boat surveys in February 2008 (n = 2), January 2009 (n = 1), January 2012 (n = 4), and January 2013 (n = 3). The mean group size during these herding activities was 17.3 individual dolphins (SD ± 7.6, n = 12, range = 9 to 30). Irrawaddy dolphins that were engaged in this type of group behavior exhibited high levels of energy, moved quickly, surfaced synchronously, and swam aggressively in a compact group. Individuals within these groups sometimes piled up on each other; and at other times, they swam abreast of each other while constantly maintaining body contact (Figure 4). While Irrawaddy dolphins are known to feed on cephalopods (Stacey & Leatherwood, 1997), this is the first description of events that occur during observed cephalopod foraging by this species in the wild. Our assumption that the Irrawaddy dolphins had been foraging and feeding on squid is supported by our findings of squid remains in the stomach contents of Irrawaddy dolphins that were collected from individuals found stranded along the Trat coastline during opportunistic beach surveys in 2008 (S. Monanunsap, pers. obs., 2008). Solitary and cooperative feeding behaviors have been observed in Irrawaddy dolphins in association with spitting water, kerplunking, mudplume feeding, shoring (Stacey & Hvenegaard, 2002; Sutaria, 2009), along with cooperative fishing-feeding with fishermen (Tint Tun, 2004), but there are no records that document foraging behavior of Irrawaddy dolphins on cephalopods associated with squid ink. The sequence of events observed during the pairmating episode, first recorded in the literature herein for this species, was only observed once and from the air. We did not observe more individual, dolphindolphin mating episodes during boat-based surveys due to the species inconspicuous behavior and the turbidity of the water in our study site. The intense social activity described herein to include herding, copulation, and mounting attempts, which we have termed as herding, was reported in other Irrawaddy dolphin populations (Kreb, 2004b; Sutaria, 2009; Minton et al., 2011). In Kalimantan, Indonesia, a mating event of coastal Irrawaddy dolphins was observed involving 13 animals displaying many of the gregarious behaviors reported herein, with the animals splitting into two subgroups thereafter (Kreb, 2004b). In Kuching,

5 Trat Irrawaddy Dolphins 405 Figure 3. Irrawaddy dolphin mating sequence Sarawak (Malaysia), large aggregations of Irrawaddy dolphins of up to 20 individuals were observed engaging in herding behavior (Minton et al., 2011). Similarly, in Chilika Lagoon, India, larger Irrawaddy

6 406 Ponnampalam et al. Figure 4. A group of Irrawaddy dolphins engaging in herd mating behavior during which the animals are mostly piled on top of each other (top) and the compact, line abreast swimming observed in herd mating groups (bottom) dolphin group sizes were documented herding one individual and showing similar synchronous and side-by-side movement between herding bouts while engaged in intense socializing (Sutaria, 2009). While the functions of these large aggregations and herding behaviors are unclear for Irrawaddy dolphins, we suggest that these social behaviors may be attributed to maintaining social bonds in an open area where levels of inter-group interactions appear to be low. Kreb (2004b) also reported that the coastal population of Irrawaddy dolphins in Kalimantan, Indonesia, had low frequencies of inter-group interactions, likely linked to the open geography of Balikpapan Bay. We observed Irrawaddy dolphins in Trat Province engaging in social behaviors, such as synchronous surfacing, petting, and contact swimming, similar to those reportedly exhibited by bottlenose dolphins (Tursiops sp.) to maintain social bonds (Connor et al., 2006a,

7 Trat Irrawaddy Dolphins b). Furthermore, it is possible that the observed herding events are to facilitate an opportunity for copulation, with the probable goal of increasing the animals chances of reproduction (Gowans et al., 2008), similar to those described in Connor (1987) and Connor et al. (1992, 2001) for bottlenose dolphins. Male bottlenose dolphins form complex super alliances to herd and abduct a female likely to be in estrus and to deny access of that female to other males (Connor et al., 1992, 2001). It remains to be seen as to whether the Irrawaddy dolphins use herding for similar reasons as bottlenose dolphins. Future research expanding on the study of social structure and associations between individuals in this area (e.g., Bejder et al., 1998; Kreb, 2004b; Sutaria, 2009; Urian et al., 2009) will give insight into how the animals interact with each other, what their mating strategies are (e.g., Kreb, 2004b; Beasley, 2007), and the drivers behind their intense social behavior. Dedicated behavioral surveys, conducted year-round, are needed to determine seasonal breeding patterns in coastal Irrawaddy dolphins. Long-term research on the distribution and behavior of these dolphins in relation to the environment is also crucial for the conservation and management of this species. Acknowledgments We would like to thank the Government of Thailand and the National Research Council of Thailand for permitting us to conduct our research in Trat Province (Permit Number 108/54). 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