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

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Harbour porpoiseThe harbour porpoise was <strong>the</strong> second most frequently seen <strong>cetacean</strong>, account<strong>in</strong>g for 2.8% <strong>of</strong> allsight<strong>in</strong>gs dur<strong>in</strong>g fast mode (T+S). Porpoises are very difficult to observe <strong>in</strong> rough wea<strong>the</strong>r (Palka,1996), and are easily missed unless sea conditions are virtually flat (e.g. sea state 2 or less). It <strong>the</strong>reforeseems likely that <strong>the</strong> average sea state <strong>of</strong> 2.75 dur<strong>in</strong>g Transects and dur<strong>in</strong>g High Effort (2.54)negatively affected <strong>the</strong> sightability <strong>of</strong> porpoises.Two porpoises were sighted on <strong>the</strong> 25 th <strong>of</strong> March with<strong>in</strong> 2 nmiles <strong>of</strong> pair trawl fisheries. The twoanimals were seen surfac<strong>in</strong>g <strong>in</strong> moderate speed not <strong>in</strong>teract<strong>in</strong>g with ei<strong>the</strong>r <strong>the</strong> fisheries or with <strong>the</strong><strong>survey</strong> vessel.Porpoises were ma<strong>in</strong>ly seen as <strong>in</strong>dividual animals, with an average group-size <strong>of</strong> 1.17 (see Table 2).The porpoises seen dur<strong>in</strong>g this <strong>survey</strong> ma<strong>in</strong>ta<strong>in</strong>ed <strong>the</strong>ir course and speed and did not approach <strong>the</strong><strong>survey</strong> vessel. The average surface water temperature for each porpoise sight<strong>in</strong>g location was 9.5°Cand <strong>the</strong> average distance to shore ranged from 4.9 to 32.7 n miles. Porpoises were seen <strong>in</strong> waters withdepths rang<strong>in</strong>g 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 <strong>of</strong> harbour porpoise sight<strong>in</strong>g location and groupsize <strong>of</strong> def<strong>in</strong>ite and probable sight<strong>in</strong>gs encountered with<strong>in</strong> <strong>the</strong> ma<strong>in</strong> <strong>survey</strong> area dur<strong>in</strong>g different effortmodes, where ‘ALL’ shows <strong>the</strong> pooled data set <strong>of</strong> T+S+TS+SLOW.Bottlenose dolph<strong>in</strong>Bottlenose dolph<strong>in</strong>s were reported twice dur<strong>in</strong>g high effort. In addition, an <strong>in</strong>cidental sight<strong>in</strong>g wasmade <strong>of</strong> a group <strong>of</strong> at least 8 tightly grouped bottlenose dolph<strong>in</strong>s <strong>in</strong> vic<strong>in</strong>ity <strong>of</strong> several pair trawl fish<strong>in</strong>gvessels which were not fish<strong>in</strong>g at <strong>the</strong> time. The animals cont<strong>in</strong>ued a moderate travel speed and did not<strong>in</strong>teract with a rigged-hulled <strong>in</strong>flatable which was stationary <strong>in</strong> <strong>the</strong> area, <strong>the</strong>y also did not <strong>in</strong>teract with<strong>the</strong> fish<strong>in</strong>g vessels or <strong>the</strong> <strong>survey</strong> vessel.The first sight<strong>in</strong>g dur<strong>in</strong>g high effort was on <strong>the</strong> 21 st <strong>of</strong> February <strong>of</strong> 2 bottlenose dolph<strong>in</strong>s approximately31 nmiles SE <strong>of</strong> Lizard Po<strong>in</strong>t. The animals were travell<strong>in</strong>g slowly and were tightly grouped. The o<strong>the</strong>rsight<strong>in</strong>g was <strong>of</strong> two bottlenose dolph<strong>in</strong>s, aga<strong>in</strong> seen travell<strong>in</strong>g slowly, on <strong>the</strong> 11 th <strong>of</strong> Marchapproximately 17 nmiles west <strong>of</strong> France (near Brest). The surface water temperature at each sight<strong>in</strong>glocation was 9.7°C and <strong>the</strong> water depth was 96.4 and 111m respectively (see Table 8).17

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