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

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Effort modeFast (S)nxSDRangeTemperature(°C)29.70.159.5-9.8Bottlenose dolphinWater depth(m)2103.77.396.4-111Distanceto shore(nmiles)2247Group size17-31Table 8. Water temperature, depth, distance to shore of bottlenose dolphin sighting location and groupsize of definite and probable sightings encountered during the survey.Risso’s dolphinRisso’s dolphins were seen once during a transit to Brest (France) on the 11 th of March approximately37.5 nmiles NW off Brest (France). The group consisted of 5 adults travelling slowly and passed thesurvey vessel at a distance of approximately 274m. The water temperature at the sighting location was10.2°C and the depth was 106m.Fin whaleOn the 11 th of March, a probable fin whale was sighted during a transit to Brest (France) approximately16.4 nmiles W off Brest. The animal surfaced twice before a deep dive. The temperature of the sightinglocation was 9.8°C and the water depth measured 111m.Relative abundanceIndices of relative abundance, calculated for different species of cetaceans encountered during transectsand high effort survey within the survey area, are presented in Table 9 with equivalent values from2004.The common dolphin had the highest relative abundance in both years. The value is higher for 2005compared to 2004. Correspondingly, the relative index of animal abundance (N/L*s, where s is themean group size) in 2005 was 84.5, which is higher than 74.5 (in 2004).Abundance estimates using Distance analysis are presented in Part 3, together with information on g(0).2200SpeciesEffortNumber ofSightings(N)RelativeAbundance(N/L)Index ofanimalAbundance(N/L * s)2004 2005 2004 2005 2004 2005Delphinus delphis T+S 100 131 11.7 16.9 74.9 84.5Phocoena phocoena T+S 12 4 1.40 0.52 2.7 0.52Tursiops truncatus T+S 2 1 0.23 0.13 2.3 0.26All cetaceans T+S 144 142 16.9 18.3Table 9. The relative abundance (N/L) of cetaceans within the survey area measured as the number ofsightings per 100km travelled, where N is the number of sightings and s is the mean group size. Pleasenote that ‘All cetaceans’ also include unidentified dolphins.18
Part 2. Fisheries observationsFishing effortDuring those parts of the survey focussed on monitoring fisheries, we recorded the position of the pairtrawlers hourly. The obtained information on ‘fishing effort’ is shown in Fig. 5, where different linesrepresent the tracks of those boats that were recorded for different pairs of trawlers (e.g. the red linesrepresent the fishing effort monitored for Scottish pair of trawlers on different days and black linesrepresent the French fishing effort). The total Fishing Effort recorded was 326 hours, of which 233hours were of French boats and 93 hours were of Scottish boats. A total of 23 hauls were monitored, 13of which were from the French fleet and 10 from the Scottish fleet (see Fig. 5).Two sub areas of fishing effort are evident, the Scottish trawlers to the north and the French Fleetfurther south. The two fleets were, for the majority, operating in different areas. The main fishingground during the 2004 survey was located further inshore and further east (see Fig. 6). During thewinter of 2004/2005 the closure of the winter sea bass pair trawl fishery within a 12 nautical milecoastal zone became active. However, a considerable overlap between an area used by both fleets andthe occurrence of common dolphins remains (see Fig. 6). Indeed the majority of dead dolphins foundfloating in the water during the 2005 survey was found within the Scottish and French Fishing grounds.Fig. 5. Fishing effort during the 2005 survey; red and black lines represent the tracks of Scottish andFrench pairs of trawlers on different days respectively, dots (similarly red and black) represent theposition of hauls19
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: Harbour porpoiseThe harbour porpois
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 and 34: DISCUSSIONThe estimated corrected d
Page 35 and 36: extrapolated total estimated mortal
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

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

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