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Marine Ecology Progress Series

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MEPS 224:305-309 (2001)  -  doi:10.3354/meps224305

A decrease in fledging body mass in common guillemot Uria aalge chicks in the Baltic Sea

Henrik Österblom1,*, Anders Bignert2, Thord Fransson3, Olof Olsson4

1Department of Vertebrate Zoology,
2Contaminant Research Group, and
3Bird Ringing Centre, Swedish Museum of Natural History, PO Box 50007, 104 05 Stockholm, Sweden
4Formas, PO Box 1206, 111 82 Stockholm, Sweden

ABSTRACT: Chick fledging body mass of the common guillemots Uria aalge breeding at Stora Karlsö in the Baltic Sea between 1989 and 2000 were studied in order to reveal any effects of an increased abundance of their main prey species, sprat Sprattus sprattus. Chick fledging body mass has decreased during the study period, and so has the condition of sprat. The deteriorated condition of the prey is most probably responsible for the observed decreased fledging body mass in guillemot chicks. This study shows that the condition of fish preyed upon by seabirds, in addition to availability, may be an important factor when studying seabird-fish interactions. It is clearly indicated that changes in the sprat population, as a consequence of changes in the Baltic Sea, have affected common guillemot fledging body mass.

KEY WORDS: Common guillemot · Uria aalge · Fledging body mass · Sprat · Baltic Sea

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