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

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

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within the Channel area. If local depletion occurs, it is not clear whether or not common dolphins fromfurther away would then start to exploit and re-populate the area. Nevertheless, the raw sighting rate(number of schools per 100km effort) is the highest rate recorded from comparable surveys in theNorth Atlantic and shows that the Channel is a very important winter habitat for common dolphins.The corrected density and abundance estimates for the winter population of short-beaked commondolphins within the current main pelagic trawl fishing grounds provide an empirical basis from whichto calculate bycatch. However, due to bias in the correction factor itself the true density and abundanceare likely to be even lower than the refined values presented here.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 bass trawl fishing grounds;3,055 (95% CI=1,425-6,544) this would equal some 52 animals. During the 2003/2004 fishing season,a bycatch of 169 common dolphins was recorded in the area in the UK bass fishery alone, producing anextrapolated 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 from 1 January 2006 are 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.4

INTRODUCTIONLittle is known about the cetacean communities in the Western Approaches of the English Channelduring winter. Indeed, only few studies to date have reported the relative abundance of the shortbeakedcommon dolphin (Delphinus delphis) in the NE Atlantic or supplied an estimate or index ofdensity and abundance (Bretagnolle et al. 2004; Hammond et al., 2002; Cañadas et al.,2004; De Boerand Simmonds, 2003; Macleod and Walker, 2004; Brereton et al., 2004). However, the majority ofthese surveys differ in distribution of effort, vessel-type, survey methodology and the season in whichthey were carried out. The conservation status of the common dolphin in this region has been of greatconcern for many years because this species is subject to bycatch in fisheries (Ross and Isaac, 2004;Tregenza and Collet, 1998; Morizur et al., 1999; Simmonds, M.P. and Hutchinson, J.D., 1994 ).The Western Approaches of the English Channel are intensively trawled by pelagic fisheries during thewinter and early spring from October to May. These fishing activities coincide with relatively highlevels of cetacean strandings. In recent years, several hundred corpses of short-beaked commondolphins (Delphinus delphis) have washed ashore in south west England each winter, many clearlydiagnosed as having died through capture in fishing nets. In the case of many of the common dolphincorpses, the external damage is consistent with death in small-meshed mobile gear (i.e. trawl netting;Sabin et al., 2003).Despite this, little bycatch monitoring has taken place in the pelagic trawl fisheries that operate in thesewaters and there is an equally inadequate understanding of the distribution and abundance of thecommon dolphin population in the area, particularly during the winter months when these fisheriesoperate. In recent years, the UK has conducted monitoring of the winter sea bass fishery, which hasbeen found to be responsible for a high rate of common dolphin bycatch (DEFRA, 2003). However,there are still no estimates of total annual bycatch for this species in all fisheries combined (ICES,2005).During the winter of 2004, WDCS and Greenpeace carried out a cetacean survey in the WesternApproaches of the English Channel (De Boer et al., 2005). The following year, February-March 2005,another survey was carried out in the same area with the main aim of collecting more information onthe little-studied cetaceans that occur in these waters at this time of year. This paper reports on thepreliminary findings of the 2005 survey and supplies preliminary comparisons for both years.All cetacean sightings made during the expedition, one blue dot presents one sighting.5

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