Szymon Bzoma
University of Gdańsk, Al. Legion�w 9, 80-441 Gdańsk, Poland

Key words: round goby, cormorants, water birds, fish-eating birds, Puck Bay, food composition.

Abstract.
This paper presents results on the food composition of cormorants feeding in the waters of the Puck Bay between February and May 1998. The results have been obtained from the analyses of 240 cormorant pellets in which 5,227 otoliths of various kinds of fish were detected. In all samples round goby were dominant, with a total of 2,224 individuals. Eelpout was the second most common type of fish found with 218 individuals The number and frequency of round goby occurrence in cormorant food increased at the beginning of April when these fish began spawning. Before April 14 its contribution to cormorant food ranged from 60% to 70% and its frequency of occurrence varied from 65% to 75%. Later, round goby constituted 90% of the fish caught by cormorants and were present in over 90% of the pellets analyzed. Also the average number of fish in single pellet increased from 6-11 to 14-16 individuals.