Cetacean Distribution & Relative Abundance Survey

Transcription

1 R.V. Pelagia NIOZ Canyons Survey Cetacean Distribution & Relative Abundance Survey & Cruise Summary Report 28 May 11 June 2007 Common Dolphins Surveyor: Dave Wall Ship Surveys Project Irish Whale and Dolphin Group

2 1. 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 II), 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 Group has conducted cetacean surveys on board commercial ferries since 2001, on board the Irish Marine Institute offshore research vessel Celtic Explorer since 2003 and on foreign research vessels commencing in 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 that 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 R.V. Pelagia during the Royal Netherlands Institute for Sea Research (NIOZ) 2007 Canyons Survey. The survey was conducted with the specific goal of targeting beaked whale species, the distribution and abundance of which are poorly understood in Irish waters and for which deep-water canyon systems are thought to provide high-value habitat. IWDG Ship Surveys Project Page 1 26/02/2008

3 2. Methods The survey was conducted on board the R.V. Pelagia as an ancillary project of the NIOZ Canyons Survey 2007 between 28 May and 11 June The survey commenced in Lisbon and covered Portuguese, Spanish and Irish Waters (survey in French waters was not possible due to bad weather). The major part of the survey was spent within the Irish EEZ, specifically within the Whittard Canyon system (fig. 2). Survey lines were opportunistic and based on predetermined locations chosen by the NIOZ for the 2007 Canyons Survey Visual Survey A single marine mammal observer was present on board during the survey and conducted watches from the monkey island located on the roof of the bridge, c10m 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 included. The observer scanned the area by eye and using 10 X 40 binoculars. Bearings to sightings were measured using a digital compass 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 and was stationary while conducting CTDs and core sampling. The vessel alternated between sampling, CTDs and steaming to the next sampling location during daylight hours. Surveying was conducted up to sea-state 6 (Beaufort scale) and in moderate to good visibility. 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 2006) Acoustic Survey A passive acoustic monitoring device for cetaceans was deployed in the Whittard Canyon. The device is a modified version of the T-POD that is used for inshore monitoring of harbour porpoise and bottlenose dolphin. The casing for the Deep POD is IWDG Ship Surveys Project Page 2 26/02/2008

4 rated to 3500m water depth and it records low frequency click trains emitted by species such as beaked whales and pilot whales. Float Recovery Line 15m Benthos Floats (-75kg) Kevlar Cable, 900m (nu 930) Benthos Floats (-50kg) Deep POD Kevlar Cable, 800m (nu 930) Bottom Weight (200kg) Fig. 1 Mooring system used to deploy Deep POD in at 800m in 1600m water depth (Mooring design by NIOZ). The Deep POD was deployed at 800m in 1,600m water depth within the Whittard Canyon system using Kevlar cable and sub-surface floats to keep the POD in a vertical position (fig. 1). Visual Survey Position & Equipment Cetacean acoustic monitoring device; Deep POD IWDG Ship Surveys Project Page 3 26/02/2008

5 The For the purposes of this survey the POD was programmed to conduct four low frequency scans (16-36KHz) for beaked whales, one mid frequency scan (22-41KHz) for beaked whales/pilot whales and one higher frequency scan (50-70KHz) for dolphins. The Deep POD was deployed on the 2 nd June and retrieved on the 9 th June. IWDG Ship Surveys Project Page 4 26/02/2008

6 3. Results: Visual Survey 3.1. Portuguese & Spanish Waters (29 th & 30 th May): Environmental Conditions Environmental data were collected at 69 stations. Survey conditions were moderate to good, with sea state 3 at only 11.6% of environmental stations and sea state 4 at 81% of stations. Visibility was good (>5km) at 89.9% of stations and moderate (1 5km) at 7.2% of stations. Light fog/mist was recorded at only one station (fig. 3). Weather conditions on the 31 st May (sea state 6 and heavy swell) did not allow for survey effort to be conducted during passage through the Bay of Biscay Cetacean Survey Results hours of survey time were logged with 15.7% (2.68hrs) of this at sea state three (Beaufort scale). 24 sightings of at least four cetacean species, totalling 276 individuals were recorded (fig. 3). Fig. 2 Visual survey effort recorded in during the current survey. (Each red dot denotes an environmental record station). IWDG Ship Surveys Project Page 5 26/02/2008

7 Identified cetacean species were common dolphin (Delphinus delphis), fin whale (Balaenoptera physalus), striped dolphin (Stenella coeruleoalba) and Sowerby s beaked whale (Mesoplodon bidens). A number of unidentified whale blows were thought to be those of fin whales. The sighting of a group of five Sowerby s Beaked Whales included two juvenile animals. Common Dolphins Fin Whale Fin whales were the most commonly encountered species, accounting for up to 62.5% of sightings (if whale blows are included). Striped dolphins were the most abundant species, accounting for 65.6% of animals counted. The high encounter rate for fin whales along the Portuguese and Spanish continental shelf edge is significant and may indicate and important feeding or migratory area for this species. No feeding behaviour was observed in fin whales at the surface, however feeding at depth might have been occurring. Fig. 3 Cetacean sightings recorded in during survey effort in Portuguese and Spanish waters. (Each square denotes a sighting of a group or an individual). IWDG Ship Surveys Project Page 6 26/02/2008

8 Seabird Activity Lists were made of all seabird species seen around the survey vessel each day, although bird counts were not conducted. Seabird diversity was low within the areas surveyed in Portuguese and Spanish waters. Four bird species were recorded: Northern Gannet (Morus bassanus), Manx Shearwater (Puffinus puffinus), Storm Petrel (Hydrobates pelagicus) and an unidentified tern species. Northern Gannet Storm Petrel A collared dove (Streptopelia decaocto) was also noted around the ship on May 30 th. Of the species encountered, only the gannet was encountered on both days of the survey in Portuguese and Spanish waters Whittard Canyon System (1 st 10 th June): Environmental Conditions Environmental data was collected at 219 stations. Survey conditions were moderate-to-good with sea state 3 at 40.6% of environmental stations and sea state 4 at 33.8% of stations. Two full days and one half day were lost to bad weather (sea state 6+, dense fog or rain). Visibility was good (>5km) at 81.7% of stations, moderate (1 5km) at 8.2% of stations and poor (<1km) at 14.2% of stations - discounting periods during which survey was suspended due to dense fog (visibility <500m). Fog/mist was recorded at 20.1% of stations (fig. 4). IWDG Ship Surveys Project Page 7 26/02/2008

9 7 6 Sea State (Beaufort 1-10) Vis (0-4) Sw ell (0-3) /05/2007 AM 29/05/2007 PM 30/05/2007 AM 30/05/2007 PM 31/05/2007 AM 31/05/2007 PM 01/06/2007 AM 01/06/2007 PM 02/06/2007 PM 02/06/2007 AM 03/06/2007 AM 03/06/2007 PM 04/06/2007 AM 04/06/2007 PM 05/06/2007 AM 05/06/2007 PM 06/06/2007 AM 06/06/2007 PM 07/06/2007 AM 07/06/2007 PM 08/06/2007 AM 08/06/2007 PM 09/06/2007 AM 09/06/2007 PM 10/06/2007 AM 10/06/2007 PM Date/Time Fig. 4 Morning and afternoon sea state, visibility and swell measurements taken daily during the survey Cetacean Survey Results 61.2 hours of survey time were logged with 15% (9.2hrs) of this at sea state three (Beaufort scale). 5 sightings of at least two cetacean species, totalling 49 individuals were recorded (fig. 5). Fig. 5 Distribution of cetacean sightings recorded within the Irish EEZ IWDG Ship Surveys Project Page 8 26/02/2008

10 Identified cetacean species were Atlantic white-sided dolphin (Lagenorhincus acutus) and long-finned pilot whale (Globicephala melas). A sighting was also made of a small, unidentified breaching cetacean. Long-finned Pilot Whale The sightings rate recorded over the Whittard Canyon system was low when compared with Spanish and Portugese waters covered by this survey and adjacent waters over the Irish continental shelf (Wall et al. 2006). Modelling of beaked whale habitat preferences by MacLeod (2005) suggest that the Whittard Canyon system should be of high habitat value for a number of beaked whale species. Despite this, no sightings were made of beaked whale species during this survey. A previous survey over deep-water canyons to the north of the Porcupine Bank (also ranked as high value habitat in the model) yielded multiple beaked whale sightings despite poorer weather conditions (IWDG 2006). MacLeaod acknowledges that the model is based primarily on benthic topography and other factors are likely to influence the use of deep-water canyon habitats by beaked whales. There is little doubt that further effort is warranted in assessing the distribution and abundance of beaked whales within deep-water canyons along the Irish shelf edge. Deep-water canyon habitats in Irish waters are difficult to access, as they lie far offshore. In addition beaked whales themselves are difficult animals to survey as they maintain a low profile in the water and require relatively calm weather to survey successfully. It is hoped that acoustic survey techniques may offer an additional tool in helping to monitor habitat use by beaked whales and to assess the value of deep-water canyon habitats to these poorly understood species Seabird Activity Seabird diversity was relatively high in the areas surveyed within the Irish EEZ. IWDG Ship Surveys Project Page 9 26/02/2008

11 Bird Species Common Tern Storm Petrel Parasitic Skua Pomarine Skua Great Skua Lessr Black-backed Gull Kittiw ake Sooty Shearw ater Manx Shearw ater Fulmar Gannet % of Days Fig. 6 Percentage of days on which 11 seabird species were recorded, during 9 survey days within the Irish EEZ. 11 seabird species were recorded (fig. 6): northern gannet (Morus bassanus), fulmar (Fulmarus glacialis), Manx shearwater (Puffinus puffinus), sooty shearwater (Puffinus griseus), kittiwake (Rissa tridactyla), lesser blackbacked gull (Larus fuscus), great skua (Stercorarius skua), pomarine skua (Stercorarius pomarinus), parasitic skua (Stercorarius parasiticus), storm petrel (Hydrobates pelagicus) and common tern (Sterna hirundo). Non-seabird species recorded were: collared dove (Streptopelia decaocto), barn swallow (Hirundo rustica), racing pigeon (Columba livia), kestrel (Falco tinnunculus), pied wagtail (Motacilla alba) and sand martin (Riparia riparia). Kittiwake Pomarine Skua IWDG Ship Surveys Project Page 10 26/02/2008

12 4. Results: Acoustic Survey The Deep POD was positioned in a branch of the Whittard Canyon system in position N W The POD was moored on the canyon floor in a water depth of 1600m (fig. 7). Fig. 7 Screen grab showing multibeam bathymetry map of deep-water canyon where Deep POD was deployed. ( Dave Wall / NIOZ) The POD recorded data on six of the eight days it was deployed. The majority of data appears to have been collected during the hours of darkness. A number of low frequency click trains (pulsed sounds emitted by cetaceans and some artificial sources) were recorded (fig. 8). Initial analysis shows that some of these click trains are from cetaceans, with pilot whales being the most likely candidate due to the long, slow nature of the click train (Nick Tregenza pers. comm.). The data also showed possible click trains from another cetacean source, however further analysis will be required to determine the origin of these click trains. Fig. 8 Screen grab showing images of low-frequency click trains recorded by Deep POD during it s deployment in the Whittard Canyon system. ( IWDG / Nick Tregenza) IWDG Ship Surveys Project Page 11 26/02/2008

13 Acknowledgements Thanks to the Royal Netherlands Institute for Sea Research (NIOZ) for accommodating this survey on board the R.V. Pelagia during the 2007 Canyons Survey (NIOZ Cruise No. 64PE269). Thanks to the captain and crew of R.V. Pelagia for their support and assistance during the survey and to Chief scientist Henko de Stigter. Preparation and deployment of the Deep POD mooring was conducted by Willem Polman. This survey was funded under the ISCOPE II project and under the Irish Foreign Research Vessel Observer Scheme. IWDG Ship Surveys Project Page 12 26/02/2008

14 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 (2006) IWDG Cetacean Sightings Database (Republic Ireland & Northern Ireland). MacLeod CD (2005) Niche Partitioning, Distribution and Competition in North Atlantic Beaked Whales. PhD thesis submitted to the School of Biological Sciences, University of Aberdeen. 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), IWDG Ship Surveys Project Page 13 26/02/2008

15 Previous IWDG Survey Reports IWDG (2007) Cetacean Distribution and Relative Abundance Survey during Rockall Trough Oceanographic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2007) Cetacean Distribution and Relative Abundance Survey during FSS Northwest Herring Acoustic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2006) Cetacean Distribution and Relative Abundance Survey during FSS Southwest Herring Acoustic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2006) Cetacean Distribution and Relative Abundance Survey during FSS Deep Water Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2005) Cetacean Distribution and Relative Abundance Survey during FSS Southwest Herring Acoustic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2005) Cetacean Distribution and Relative Abundance Survey during Irish Seabed Survey: Leg 17. Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2004) Summer Distribution and Relative Abundance of Cetaceans off the West Coast of Ireland. Final report to the Heritage Council, Kilkenny, Ireland. IWDG (2004) Cetacean Distribution and Relative Abundance Survey during FSS Northwest Herring Acoustic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2004) Cetacean Distribution and Relative Abundance Survey during FSS Blue Whiting Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2004) Cetacean Distribution and Relative Abundance Survey during the Celtic Sea Herring Acoustic Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG (2003) Cetacean Distribution & Relative Abundance Survey during Ground fish Survey Unpublished Report to the Marine Institute, Oranmore, Galway, Ireland. IWDG Ship Surveys Project Page 14 26/02/2008

16 Appendix II: List of cetacean species recorded in Irish waters. Atlantic White-Sided Dolphin Lagenorhynchus actus Beluga Delphinapterus leucas Blue Whale Balaenoptera musculus Bottlenose Dolphin Tursiops truncatus Common Dolphin Delphis delphis Cuvier's Beaked Whale Ziphius cavirostris False Killer Whale Pseudorca crassidens Fin Whale Balaenoptera physalus Gervais Beaked Whale Mesplodon europaeus* Harbour Porpoise Phocoena phocoena Humpback Whale Megaptera novaeangliae Killer Whale Orcinus orca Minke Whale Balaenoptera acutorostrata Northern Bottlenose Whale Hyperoodon ampullatus Northern Right Whale Eubalaena glacialis Pilot Whale (long-finned) Globicephala melas Pygmy Sperm Whale Kogia breviceps Risso's Dolphin Grampus griseus Sei Whale Balaenoptera borealis Sowerby's Beaked Whale Mesplodon bidens Sperm Whale Physeter macrocephalus Striped Dolphin Stenella coeruleoalba True's Beaked Whale Mesplodon mirus White-Beaked Dolphin Lagenorhynchus albirostris Vagrant * Recorded only from Stranding IWDG Ship Surveys Project Page 15 26/02/2008