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

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BehaviourDescriptionT+S%SLOW+TS%FOS%’04 ’05 ’04 ’05 ’04 ’05Travel fast Fast speed in a given direction 16.7 17.5 11.4 11.5 11.1 -TravelTravel Cruising speed in a given direction 9.9 17.5 2.3 15.4 8.9 -MediumTravel slow Slow movement in a given direction 6.8 12 27.3 15.4 22.2 -MillingSlow movement not in any 1.2 0.43 2.3 3.8 6.7 -particular direction, showingfrequent changes in their headingLooseOne group of animals which is 9.3 20.1 18.2 23.1 2.2 -loosely grouped, e.g. animals aremore than 2-5 body lengths fromeach otherTightOne group of animals which remain 9.9 15.8 18.2 7.7 4.4 -in a tight group formation, e.g.within one body length from eachotherSpread out No obvious group formations, e.g. 0.6 1.3 - - - -Group>5 body lengths from each otherGroups Loose Different groups are in the area, buteach group is loosely grouped, e.g.animals within each group are morethan 2-5 body lengths from eachother4.9 - - - - -Groups tight Different groups are in the area, but 1.2 0.85 - 3.8 2.2 -each group is tight, e.g. animalswithin each group are within onebody length from each otherPorpoising High surfacing during fast 16.1 1.3 2.3 - 24.4 -swimming, with half of body widthor more in airFull Breach Lifting the whole body above 8 1.3 4.6 - - -surface. Noisy re-entry by hitting thesurface with the lateral body surfaceLogging Motionless at the surface for some 0.6 - - - - -seconds, blowhole above surfaceBow ride Gliding/swimming on pressure wave 10.3 7.7 11.4 19.2 8.9 -in front of boatWake ride Gliding/swimming on pressure wake - 1.3 - - -SurfaceFeeding(behind boat)Dolphins involved in any effort to 0.6 0.85 - - 6.7 -capture prey as evidenced bychasing fish, co-ordinated deepdiving and rapid direction changesScouting Brief approach toward the vessel up 0.6 0.85 2.3 - 2.2 -to a few metres and then movingawaySpy hop Head and eyes above water, headvertical0.6 - - - - -Sharking Swimming below the surface 2.5 1.3 - - - -showing the dorsal fin, often makingrapid directional changesTable 6. Percentages of different reported behaviours for common dolphins during fast survey modes (T+S), slowsurvey modes (SLOW+TS) and during Fisheries Observations (FOS). Behaviours were reported when dolphinswere sighted first and when changes in behaviour occurred these were entered as re-sightings. For convenience theshaded boxes highlight the highest percentages within each column.16
Harbour porpoiseThe harbour porpoise was the second most frequently seen cetacean, accounting for 2.8% of allsightings during fast mode (T+S). Porpoises are very difficult to observe in rough weather (Palka,1996), and are easily missed unless sea conditions are virtually flat (e.g. sea state 2 or less). It thereforeseems likely that the average sea state of 2.75 during Transects and during High Effort (2.54)negatively affected the sightability of porpoises.Two porpoises were sighted on the 25 th of March within 2 nmiles of pair trawl fisheries. The twoanimals were seen surfacing in moderate speed not interacting with either the fisheries or with thesurvey vessel.Porpoises were mainly seen as individual animals, with an average group-size of 1.17 (see Table 2).The porpoises seen during this survey maintained their course and speed and did not approach thesurvey vessel. The average surface water temperature for each porpoise sighting location was 9.5°Cand the average distance to shore ranged from 4.9 to 32.7 n miles. Porpoises were seen in waters withdepths ranging from 30 to 96.4m (see Table 7).Effort modeFast (T+S)Slow (TS+SLOW)ALLnxSDRangenxSDRangenxSDRangeTemperature(°C)49.60.618.7-10.329.40.159.2-9.569.50.528.7-10.3Harbour porpoiseWater depth(m)467.924.630-96.4283.311.172.2-94.3673.122.530-96.4Distanceto shore(nmiles)419.512.14.9-32.7225.91.5524.3-27.4621.610.34Group size410021.50.51-261.170.371-24.9-32.7Table 7. Water temperature, depth, distance to shore of harbour porpoise sighting location and groupsize of definite and probable sightings encountered within the main survey area during different effortmodes, where ‘ALL’ shows the pooled data set of T+S+TS+SLOW.Bottlenose dolphinBottlenose dolphins were reported twice during high effort. In addition, an incidental sighting wasmade of a group of at least 8 tightly grouped bottlenose dolphins in vicinity of several pair trawl fishingvessels which were not fishing at the time. The animals continued a moderate travel speed and did notinteract with a rigged-hulled inflatable which was stationary in the area, they also did not interact withthe fishing vessels or the survey vessel.The first sighting during high effort was on the 21 st of February of 2 bottlenose dolphins approximately31 nmiles SE of Lizard Point. The animals were travelling slowly and were tightly grouped. The othersighting was of two bottlenose dolphins, again seen travelling slowly, on the 11 th of Marchapproximately 17 nmiles west of France (near Brest). The surface water temperature at each sightinglocation was 9.7°C and the water depth was 96.4 and 111m respectively (see Table 8).17
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: Initial sighting cuesDuring fast su
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

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

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