Report of a cetacean survey in the Western Approaches of the ...

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Proportion of primary sighting bearings madeduring double platform effort0.250.2Proportion0.150.10.0500-10 10-2020-3030-4040-5050-6060-7070-8080-9090-100>100Bearing categoryFig. 20. Proportion of primary sighting bearings made during double platform effort fordifferent bearing categories.More common dolphin calves and juveniles were sighted during the 2005 survey, particularly inStratum E and further inshore. In New Zealand the presence of a postanal hump has been reported as atool to identify sexually mature male short-beaked common dolphins (Neuman et al., 2002). Indeed,dead mature male common dolphins that were examined during the survey showed the presence of apostanal hump, however in the animals examined it was not as pronounced as the New Zealanddolphins. Photographs and underwater video footage of alive dolphins also obtained good images ofpostanal humps, and these are currently further analysed in order to help to characterise the schoolcomposition of common dolphins.During fisheries observations, a total of 20 sightings of cetaceans (of which 15 sightings were commondolphins) were reported. Interactions between fisheries and cetaceans were reported four times duringwhich common dolphins were seen around the trawlers during the setting and towing procedures.CONCLUSIONSThe winter diversity of the cetacean community in the Western Approaches of the English Channel,with a total of 7 different species seen during both surveys, highlights the fact that the area includesimportant winter cetacean habitats.The population estimates calculated for the strata provide a reference for comparison with estimatedbycatch removals and future studies. The results clearly show that responsive movement towards thevessel is an important consideration for surveys of common dolphins. In particular, it seems likely thatsurveys relying purely on naked eye observations are unlikely to give reliable results. However, thenarrow angle of observations of the Tracker observers on this survey probably resulted in anunderestimate of the strip width and so it is likely that the estimates presented are still positively biaseddue to responsive movement. Although sample sizes were rather small, the results suggest that the7x50 binoculars may have been adequate to detect common dolphins prior to responsive movement toour survey vessel, at least at lower sea states. However, this distance may be vessel specific and theuse of higher powered binoculars should be considered wherever possible.A bycatch level for small cetaceans of more than 1.7% of the best available estimate of abundance hasbeen deemed in international fora to be unacceptable (ASCOBANS, 2000). Based on our pooledcorrected estimate for Stratum E (the area overlapping with the current main fishing grounds; 3,055(95% CI=1,425-6,544) this would equal some 52 animals. During the 2003/2004 fishing season, abycatch of 169 common dolphins was recorded in the area in the UK bass fishery alone, producing an34
extrapolated total estimated mortality for the UK fishery of 439 animals (SMRU, 2004). During the2004/2005 fishing season, a bycatch of 95 common dolphins was recorded, producing an extrapolatedtotal estimated mortality of 139 animals (SMRU, 2005).A more comprehensive and wide-ranging assessment of bycatch levels is urgently needed. As a resultof EU legislation, statistically robust observer programs should have been introduced in the pelagictrawl fisheries in this area from 1 January 2005. However, the requirement for observation of the gilland tanglenet fisheries in this area which will, from 1 January 2006, be required to deploy pingers, ismuch less stringent, and non-existent for vessels of less than 12m.The data from this survey show that the Channel is a very important winter habitat for commondolphins. If this area is only used by a subset of the total Northeast Atlantic ‘stock’ of commondolphins as seems most likely, and this may be a distinct population which returns each year, then thereis, at the very least, a risk of localised depletion within the Channel area as a result of bycatch.CREDITS AND ACKNOWLEDGEMENTSThis report has been written by M. N. de Boer, S. Keith and M. P. Simmonds. Analytical advice waskindly provided by R. Leaper (facilitated by the financial support of IFAW) and Cara Miller. The postmortem results reported here in the attached annex were kindly supplied by the team at the Institute ofZoology. The primary authors are grateful to all contributors and advisers. Any mistakes are of courseour own and we would be grateful for any feedback, which may be sent to marks@wdcs.org.We would like to thank everyone – including volunteers, WDCS staff, Greenpeace crew and Captain F.Kamp of the MV Esperanza – who helped to make this survey possible. Our thanks also to SarahDuthie for her support and to the Greenpeace photographers Gavin Newman and Kate Davison, whotook photographs and film. Many thanks also to Captain Keith Reeves (Orca Sea-faris, Falmouth) forhelp with retrieving a dead dolphin and to the Cornwall Wildlife Trust Marine Strandings Network.This study was funded by the Greenpeace Environmental Trust and WDCS, the Whale and DolphinConservation Society.REFERENCESASCOBANS, 2000. Resolution on incidental take of small cetaceans. Annex 9c of Proceedings of theThird Meeting of the Parties. Bristol UK.Brereton, T.M., Williams, A.D., Martin, C. 2004. Ecology and status of the common dolphin Delphinusdelphis in the English Channel and Bay of Biscay1995-2002.Bretagnolle, V., Certain, G., Houte, S., Métais, M. 2004. Distribution maps and minimumabundanceestimates for wintering auks in the Bay of Biscay, based on aerial surveys. Aquatic LivingResource, 17:353-360Buckland, S.T. and Turnock, B.J. 1992. A robust line transect method. Biometrics, 48:901-909Buckland, S.T., Anderson, D.R., Burnham, K.P., Laake, J.L, Borchers, D.L. and L. Thomas. 2002.Introduction to Distance sampling: estimating abundance of biological populations. Oxford UniversityPress Inc., New York.Cañadas, A., Desportes, G., Borchers, D. 2004. The Estimation of the detection function and g(0) forshort-beaked common dolphins (Delphinus delphis) using double platform data collected during theNASS-95 Faroese survey. J. Cetacean Res. Manage. 6:191-198.Dawson, S., Slooten, E., DuFresne, S., Wade, P. Clement, D. 2004. Small-boat surveys for coastaldolphins: line-transect surveys for Hector’s dolphins (Cephalorhynchus hectori). Fish. Bull. 201:441-451.35
Page 1 and 2: Report of a cetacean survey in theW
Page 3 and 4: EXECUTIVE SUMMARYThe Western Approa
Page 5 and 6: INTRODUCTIONLittle is known about t
Page 7 and 8: Two important assumptions of line t
Page 9 and 10: also to report the presence of dolp
Page 11 and 12: RESULTSPart 1. Cetacean distributio
Page 13 and 14: SpeciesFAST MODENumber of sightings
Page 15 and 16: Initial sighting cuesDuring fast su
Page 17 and 18: Harbour porpoiseThe harbour porpois
Page 19 and 20: Part 2. Fisheries observationsFishi
Page 21 and 22: On the 23 rd of March, at 08:23, a
Page 23 and 24: Fig 7. Frequency distribution of si
Page 25 and 26: The estimates of abundance generate
Page 27 and 28: Proportion of sightings by perpendi
Page 29 and 30: Proportion of sightings by componen
Page 31 and 32: Fig. 18. Histograms of perpendicula
Page 33: DISCUSSIONThe estimated corrected d
Page 37 and 38: Tregenza, N.J.C. and Collet, A. 199
Page 39 and 40: Dolphin 2SPECIES: Common dolphin (D
Page 41 and 42: CETACEAN POSTMORTEM REPORTDolphin 7

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