Verspreiding van Alkachtigen Alcidae voor de Britse oostkust, nazomer 1987 en ’88
Sula , Volume 3 - Issue 3 p. 89- 105
In this paper the results of ship-based counts of Alcidae at sea in late summer 1987 and 1988 off the British east coast are presented. Densities of Razorbills Alca torda, Guillemots Uria aalge and Puffins Fratercula arctica are mapped (figures 1-10) and listed (tables 1-3) for four trips to the waters east of the British Isles: 10-24 August 1987 (265 km² surveyed, figures 1-3), 6 and 9-24 September 1987 (365 km² surveyed, figures 4-6), 7-8 September 1987 (77 km² surveyed, figure 7), and 5-29 September 1988 (537 km² surveyed, figures 8-10). Methods used are essentially the same as used by the Seabirds At Sea Team (SAST) and the results are therefore fully comparable. Counts were conducted on board the fishery research vessel MV Tridens during surveys of Herring Clupea harengus larvae. Densities (number of birds per km²) are presented per 6’N x 10’E/W square (115 km² at 56°N; figures 1-10) or summarized for certain transects (tables 1-3). (10-24 August 1987) Highest densities for all three species in the Aberdeen Bank area, where a high primary production and rich feeding areas for seabirds are known to occur. An other reason for the high densities of auks in these waters is the presence of some important breeding colonies nearby. Razorbills were comparatively scarce. SAST-data suggest that much larger numbers are to be found just to the west and northwest of our study area. Offshore, Guillemots were slightly more abundant, particularly in the Dogger Bank area, in comparison with earlier surveys by SAST. (6 and 9-24 September 1987) Again highest densities of Guillemots in the Aberdeen Bank area and off the Firth of Forth. Guillemots outnumber Razorbills and Puffins in all sectors and Razorbills are scarce south of the Aberdeen Bank area. (7-8 September 1987) Two days were spent in waters between Orkney and Shetland (figure 7). Razorbills and Guillemots were common (3.85 and 10.31/km² respectively) but Puffins were rare. Densities of Razorbills and Guillemots were high compared with SAST counts, where the majority was found to have left these waters at this time of year. (5-29 September 1988) Razorbills and Guillemots were abundant in the northernmost sectors, notably in the Aberdeen Bank area (Razorbill up to 50/km², Guillemot up to 200/km²). Further south, high densities were only found close inshore the English east coast. Puffins were distributed more widely in both the northerly and southerly sectors, with little or no difference in mean numbers per km². According to older SAST data, larger numbers were to be expected in waters just between our ’northerly’ and ’southerly’ sectors. It is concluded that the data presented here agree well with those published by SAST for August and September. Densities of Guillemots in the offshore zone were slightly higher now and Razorbills and Guillemots were more abundant in September near Orkney and Shetland than expected.
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