Connectivity and age distributionof the Baltic Common Guillemot Uria aalge population:evidence from morphometry and ringing recoveries

摘要

In evolutionary ecology, environmental monitoring and conservation manage-ment, reliable information on phenotypic and demographic traits in marine seabirds is highly wanted, but difficult to acquire. Therefore, freshly dead Common Guillemots Uria aalge (n = 149) incidentally drowned in salmon drift gill nets in the Baltic Sea, during October–November, were studied. We noted age, sex, moult pattern and fat status, and took morphometric measurements to compare with data from the Northeast Atlantic population. Only minor pheno-typic differences were found. The birds had slightly longer wings than expected at the latitude where they were collected, probably due to their newly grown pri-maries and/or observer differences, rather than a genetic divergence. The Baltic Guillemot appears not to be a distinct subspecies, but only the marginal member of a deme. Ringing recoveries also suggest intermittent exchange of birds between the Baltic and the North Sea. Young birds did not seem to be over-represented in gill net bycatches. Our found age distribution – with a heavy dominance of adult birds, but few immature/juveniles – deviated from that reported earlier, and suggests that the population is more vulnerable to adult mortality through bycatch in gill nets than previously believed