Cetacean Distribution & Relative Abundance Survey

Transcription

1 R.V. Celtic Explorer Rockall Trough Oceanographic Survey Cetacean Distribution & Relative Abundance Survey 24 January 2 February 2007 Surveyor: Dave Wall Ship Surveys Unit Irish Whale and Dolphin Group

2 Introduction The waters of Ireland s Exclusive Economic Zone (EEZ) are thought to represent one of the most important cetacean (whales, dolphins and porpoise) habitats in Europe. To date 24 species of cetacean have been recorded (Appendix I), with seven of these having been confirmed as calving within the Irish EEZ, while a number of other species are possibly calving (e.g. minke whale and northern bottlenose whale) (Berrow 2001). In recognition of their importance for cetaceans, the Irish government declared all Irish waters (within the EEZ) to be a whale and dolphin sanctuary in 1991 (Rogan and Berrow 1995). Despite this recognition, information on the distribution and relative abundance of cetaceans within the Irish EEZ, especially in offshore waters, is very limited (Wall et al. 2006). The Irish Whale and Dolphin Group (IWDG) have been collecting data on the distribution and relative abundance of cetaceans in Irish waters (including Northern Ireland) since The IWDG casual and constant effort sightings schemes record data mainly from land-based sightings and surveys (Berrow et al. 2001). The IWDG has conducted cetacean surveys on board commercial ferries since 2001 and on board the Irish Marine Institute s offshore research vessel Celtic Explorer since In 2003, the IWDG initiated the Irish Scheme for Cetacean Observation and Public Education (ISCOPE), which aimed to promote better awareness and knowledge of cetaceans (whales, dolphins and porpoises) in Irish waters, by encouraging public participation in cetacean recording. Under ISCOPE II, the IWDG are committed to filling in data gaps which exist in our knowledge of the seasonal distribution and abundance of cetaceans in offshore habitats. As part of this project the IWDG conducted a cetacean distribution and relative abundance survey on board the RV Celtic Explorer during the Marine Institute s 2007 Rockall Trough Oceanographic Survey. IWDG Ship Surveys Unit Page 1 19/04/2008

3 Methods The survey was conducted on board the R.V. Celtic Explorer as an ancillary project of the Rockall Trough Oceanographic Survey between 24 January and 2 February The survey covered areas of the Porcupine Bank, Rockall Trough, Rockall Bank and the continental shelf to the west of Erris. The survey areas were opportunistic and based on predetermined locations chosen by the Marine Institute for the 2007 Rockall Trough Oceanographic Survey. A single marine mammal observer was present on board during the survey and conducted watches from the crow s nest located above the bridge, 18m above sea level. Observer effort focused on a 90 degree arc ahead of the ship; however sightings located up to 90 degrees to port and starboard were also included. The observer scanned the area by eye and using 10 X 40 binoculars. Bearings to sightings were measured using an angle board and distances were estimated with the aid of distance measuring stick. Environmental data were recorded every 15 minutes using Logger 2000 software (IFAW 2000). Sightings were also recorded using Logger Automated position data were obtained through a laptop computer linked to a GPS Receiver Unit. The survey vessel travelled at an average speed of 10 knots when steaming (except where restricted due to heavy weather). The vessel stopped on a regular basis to conduct CTDs or grab samples. During these times the vessel remained stationary for up to 2½ hours at a time (when in deep water). Because this survey was conducted in winter where poor weather is the norm, surveying was conducted in all sea states (provided it was safe to do so) and in moderate to good visibility. This was justified on the basis that all cetacean distribution data from the poorly surveyed winter season is of value. As this was a survey onboard a vessel of opportunity, the survey was conducted in passing mode and cetaceans sighted were not approached. Sightings were identified to species level where possible, with species identifications being graded as definite, probable or possible. Where species identification could not be confirmed, sightings were downgraded (e.g. unidentified dolphin / unidentified whale / unidentified beaked whale etc.) according to criteria established for the IWDG s cetacean sightings database (IWDG 2007). IWDG Ship Surveys Unit Page 2 19/04/2008

4 Results Environmental Conditions Environmental data was collected at 195 stations. Survey conditions were very good for the first two days, with sea states 2-3. For the latter part of the survey sea states increased and were accompanied by a growing swell. Maximum daily wind speeds exceeded 35knots on 50 of days. Sea state was 3 at 39.5% of environmental stations (60.5% sea state 4-6). One full day was lost to bad weather (where it was unsafe to ascend to the crow s nest). Visibility was good (>5km) at 79% of stations, moderate (1 5km) at 18.5% of stations and poor (<1km) at 2.5% of stations - discounting periods during which survey was suspended due to dense fog or heavy rain (visibility <500m). A heavy swell (2m+) was recorded at 16.4% of stations. Rainfall was recorded at 2.6% of stations and fog/mist was recorded at 1% of stations (figs. 1-3) Wind Speed (Kn) Av Wind Speed Max Wind Speed AM PM AM PM AM PM AM PM AM PM AM PM AM PM AM PM Date/Time Fig. 1: Average morning and afternoon wind speeds and maximum daily wind speeds recorded by ships weather station. (Wind speed given in knots). IWDG Ship Surveys Unit Page 3 19/04/2008

5 Degrees Wind Direction AM PM AM PM AM PM AM PM AM PM AM PM AM PM AM PM Date/Time Fig. 2: Wind direction and recorded by ships weather station. (Wind direction given in compass degrees) Sea State (Beaufort) Visibility (1-3) Sw ell Height (1-3) AM PM AM PM AM PM AM PM AM PM AM PM AM PM AM PM Date/Time Fig. 3: Sea state, visibility and swell height recorded during survey effort. IWDG Ship Surveys Unit Page 4 19/04/2008

6 Cetacean Survey Results 42.8 hours of survey time were logged with 39.8% (17.05hrs) of this at Beaufort sea state three (fig. 4). Fig. 4: Survey effort from Three cetacean species common dolphin (Delphinus delphis), pilot whale (Globicephala melas) and fin whale (Balaenoptera physalus) - were sighted during the survey (fig. 5). Additional sightings were made of unidentified dolphins (thought to be common dolphins) over the continental shelf. Sightings of dolphin species occurred over the continental shelf and porcupine bank whereas all pilot whale sightings occurred over the slopes of the continental shelf edge, which are considered the preferred habitat for this species. One whale sighting occurred over the continental shelf and one in the Rockall Trough. Fin whales occur commonly off the south coast during the autumn and winter months but sightings of this species have been made off all Irish coasts and in offshore waters over the Rockall Bank. No sightings of cetaceans were made over the Rockall Bank, however survey conditions were not good during the period spent over the eastern edge of the bank slopes. Atlantic white IWDG Ship Surveys Unit Page 5 19/04/2008

7 sided dolphins commonly occur in the waters over the Rockall Bank (Wall et al 2006), however sightings tend to occur in shallower waters (< 350m) not covered during this survey. Fig. 5: Locations of cetacean sightings recorded during the survey. Bird Activity Species lists were made of all bird species seen around the survey vessel each day. 10 bird species were recorded during the survey (fig. 6). Four of these were seen on a regular basis: Kittiwake (Rissa tridactyla), great black-backed gull (Larus marinus), fulmar (Fulmarus glacialis) and gannet (Morus bassanus). Kittiwake was the only species to be encountered on all days at sea. Fulmar and gannet were both encountered on all but one day. Other species recorded were guillemot (Uria aalge), great skua (Stercorarius skua), glaucous gull (Larus hyperboreus), herring gull (Larus argentatus), lesser black-backed gull (Larus fuscus) and shag (Phalacrocorax aristotelis). IWDG Ship Surveys Unit Page 6 19/04/2008

8 Shag Great Skua Glaucous Gull Herring Gull Bird Species Great Black-backed Gull Lesser Black-backed Gull % of Days Kittiw ake Fulmar Gannet Auk Species (All) % of Days Fig. 6: Percentage of days on which 10 bird species were recorded during 7 survey days. IWDG Ship Surveys Unit Page 7 19/04/2008

9 References Berrow, S.D., Whooley, P. and Ferriss, S. (2001) Irish Whale and Dolphin Group cetacean sighting schemes: development of a system to record sightings of cetaceans (whales, dolphins and porpoises) in Irish waters. Final report to the Heritage Council (Ireland), Kilkenny. IFAW (2000) Logger 2000 software. Inter-national Fund for Animal Welfare, London. IWDG (2007) IWDG Cetacean Sightings Database (Rep. Ireland & Northern Ireland). Rogan, E. and Berrow, S.D. (1995) The management of Irish waters as a whale and dolphin sanctuary. In A.S. Blix, L. Walløe and Ø. Ulltang (eds), Whales, seals, fish and man, Amsterdam. Elsevier Science. Wall D., O Brien J., Meade J. & Allen B.M. (2006) Summer distribution and relative abundance of cetaceans off the west coast of Ireland. Biology and Environment: Proceedings of the Royal Irish Academy, 106B (2), Previous IWDG Survey Reports IWDG (2007) Cetacean Distribution and Relative Abundance Survey during FSS Northwest Herring acoustic Survey Unpublished Report to the Marine Institute. IWDG (2006a) Cetacean Distribution and Relative Abundance Survey during FSS Deepwater Survey Unpublished Report to the Marine Institute. IWDG (2006b) Cetacean Distribution and Relative Abundance Survey during FSS Southwest Herring Acoustic Survey Unpublished Report to the Marine Institute. IWDG (2005a) Cetacean Distribution and Relative Abundance Survey during Celtic Sea Herring Acoustic Survey Unpublished Report to the Marine Institute. IWDG (2005b) Cetacean Distribution and Relative Abundance Survey during Irish Seabed Survey: Leg 17. Unpublished Report to the Marine Institute. IWDG (2004a) Summer Distribution and Relative Abundance of Cetaceans off the West Coast of Ireland. Report to the Heritage Council. IWDG (2004b) Cetacean Distribution and Relative Abundance Survey during North-west Herring Acoustic Survey IWDG Ship Surveys Unit Page 8 19/04/2008

10 IWDG (2004c) Cetacean Distribution and Relative Abundance Survey during Blue Whiting Survey IWDG (2004) Cetacean Distribution and Relative Abundance Survey during the Celtic Sea Herring Acoustic Survey IWDG (2003) Cetacean Distribution & Relative Abundance Survey during Ground fish Survey Unpublished survey report, Marine Institute, Galway. IWDG Ship Surveys Unit Page 9 19/04/2008

11 Appendix I: List of cetacean species recorded in Irish waters. Atlantic White-Sided Dolphin Beluga Blue Whale Bottlenose Dolphin Common Dolphin Cuvier's Beaked Whale False Killer Whale Fin Whale Gervais Beaked Whale Harbour Porpoise Humpback Whale Killer Whale Minke Whale Northern Bottlenose Whale Northern Right Whale Pilot Whale (long-finned) Pygmy Sperm Whale Risso's Dolphin Sei Whale Sowerby's Beaked Whale Sperm Whale Striped Dolphin True's Beaked Whale White-Beaked Dolphin Lagenorhynchus actus Delphinapterus leucas Balaenoptera musculus Tursiops truncatus Delphis delphis Ziphius cavirostris Pseudorca crassidens Balaenoptera physalus Mesplodon europaeus Phocoena phocoena Megaptera novaeangliae Orcinus orca Balaenoptera acutorostrata Hyperoodon ampullatus Eubalaena glacialis Globicephala melas Kogia breviceps Grampus griseus Balaenoptera borealis Mesplodon bidens Physeter macrocephalus Stenella coeruleoalba Mesplodon mirus Lagenorhynchus albirostris IWDG Ship Surveys Unit Page 10 19/04/2008