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

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Common dolphinOverall, common dolphins comprised 89.8% of all cetacean sightings made within the survey area. Atotal of 79 sightings were made during transects (T) and an additional 52 sightings during high effort.Additionally, 74 incidental sightings of approximately 406 animals were made throughout the voyageand a total of 15 fisheries related sightings were made of approximately 52 animals.Common dolphins were sighted in waters with an average sea surface temperature of 9.4°C (rangefrom 8.1-10.3) and, on average, were sighted 14.5 nautical miles from the coast which is similar to lastyear’s findings (see Table 4). All common dolphin sightings related with fisheries were seen beyondthe UK’s 12nmile coastal zone, with an average distance to shore of 27 nmiles (SD 6.9, n 15).Water depths measured at each sighting location averaged 68.6m for this species, ranging from 30-96.4m (see Table 4).Common dolphins were encountered in groups, ranging up to 22 animals (best estimate), with anaverage group size of 5, although a group of up to 30 animals (maximum estimate) was reported on oneoccasion.Effort modeFast (T+S)Slow(TS+SLOW)Fisheries(FOS)ALLnxSDRangenxSDRangenxSDRangenxSDRangeTemperature(°C)Common dolphinWater depth(m)Distanceto shore(nmiles)Group size2004 2005 2004 2005 2004 2005 2004 2005689.380.668-10.3199.070.678.1-9.9309.360.418-101179.320.618-10.3949.40.638.1-10.368.60.837.8-9.58575.828.0161-93.91666.029.5443.9-81.30 1273.166.767.9-921009.380.678.1-10.311273.6210.543.9-93.911269.115.730-96.4660.431.332.2-94.310013.026.053.29-32.12514.316.572.8-20.50 3019.465.7614-37.911868.616.830-96.415514.516.542.8-37.913014.98.94-40.71211.39.93.3-311006.48.481-45265.736.971-330 3011.5312.491-4514214.59.13.3-40.7Table 4. Water temperature, depth, distance to shore of common dolphin sighting location and groupsize of definite and probable sightings encountered within the main survey area during different effortmodes, where ‘ALL’ represents pooled effort.Common dolphins often approached the survey vessel to bow or wake-ride, and were also sometimesseen to remain at a distance. Groups containing juveniles and calves were encountered on 44 occasions,of which 15 juveniles and 5 calves were seen during Transect and High effort. The percentage of calvesand juveniles was 3.1% during both Transect (T) and High Effort modes (S), which was highercompared than the 2004 survey (2.3%). Most calves and juveniles were recorded within stratum E,although occasionally calves were seen further inshore or elsewhere within the survey area (see Fig. 4).1557.328.271-4512554.21-22125.754.11-15013754.21-2214
Initial sighting cuesDuring fast survey modes (T+S) ‘back’ was reported as an initial cue more than other cues (sample sizen=116), which is similar to the 2004 findings. However, the sample size during ‘slow speed’ isparticularly low (n=11; see Table 5).Initial CueT+S%SLOW+TS%FOS%2004 2005 2004 2005 2004 2005Back/dorsal 44 44 65 64 66 -Splash 23 24 4 36 7 -Breach 22 17 23 0 7 -Birds - 1 - 0 - -Underwater 6 2 8 0 - -Blank (no cue reported) 5 12 - 0 20 -Table 5. Percentage of initial cues reported for sightings of common dolphins made during differentsurvey modes, e.g. fast mode (T+S), slow mode (SLOW+TS) and fisheries observations (FOS).Please note the rather low sample size (n=11) during slow speed mode (SLOW+TS) in 2005.Fig. 4. Common dolphin calves and juveniles recorded throughout the survey.Observed behaviourDuring fast speed modes (T+S), the most frequently reported behaviours of common dolphins werethose of travelling fast (17.5% of all reported behaviours) or at moderate speed (17.5%, see Table 6).Bow-riding comprised about 10.3% of all behaviours and animals were reported either in a tightlygrouped composition (9.9%) or as ‘Loose’ (9.3%, see Table 6). During slow survey modes(SLOW+TS), the most frequently encountered travel speed was moderate to slow (15.4%) with aloosely grouped composition (23.1%). Furthermore, the animals were actively involved in bow ridingthe vessel (19.2%; see Table 6).15
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: SpeciesFAST MODENumber of sightings
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 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

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