Influence of hydrography, fishing activity, and colony location on summer seabird distribution in the south-eastern North Sea
Possible determinants of the distribution of 11 species of seabird in the south-eastern North Sea were investigated in July 1993 and 1994. During ship transects in both years, seabird distribution, trawling activity, and hydrographic parameters (salinity, temperature, stratification/mixing, water de...
| Published in: | ICES Journal of Marine Science |
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| Main Author: | |
| Format: | Text |
| Language: | English |
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Oxford University Press
1997
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| Online Access: | http://icesjms.oxfordjournals.org/cgi/content/short/54/4/566 https://doi.org/10.1006/jmsc.1997.0253 |
| Summary: | Possible determinants of the distribution of 11 species of seabird in the south-eastern North Sea were investigated in July 1993 and 1994. During ship transects in both years, seabird distribution, trawling activity, and hydrographic parameters (salinity, temperature, stratification/mixing, water depth, water clarity) were measured. Analysis of environmental and seabird density variables by principal component analysis revealed seven components, explaining 71% of the variance found in all variables. The most important components were: (1) a land–sea gradient combining hydrographic properties and distance to land/nearest colony; (2) trawler abundance; and (3) a factor linked to water stratification and surface temperature. Distance to colony had a significant influence on the densities of all nine breeding species considered. Flight radii differed considerably between the species. Densities in the vicinity of trawlers were particularly high in black-headed gulls ( Larus ridibundus ), herring gulls ( L. argentatus ), and great black-backed gulls ( L. marinus ). Black-headed gulls and herring gulls had the highest proportion of ship-followers of the total number of seabirds at sea; no ship-followers at all were found in Sandwich terns ( Sterna sandvicensis ), common/Arctic terns ( S. hirundo / paradisaea ), or guillemots ( Uria aalge ). Surface salinity, transparency, and thermal stratification were apparently the most important hydrographic properties, characterizing distinct water masses. Cluster analysis revealed a group of four offshore species ( Fulmarus glacialis , Uria aalge , Rissa tridactyla , Larus fuscus ) and seven inshore species ( Larus ridibundus , L. canus , L. marinus , L. argentatus , Sterna sandvicensis , S. hirundo / paradisaea ). Relations between important abiotic parameters and seabird diet are discussed. |
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