Diet of Common Murres Wintering in the Northern Skagerrak during 1988-1990: Variation with Sex, Age and Season

Abstract

-The winter diet of 522 Common Murres ( Uria aalge) killed in fishing nets off Ostfold, SE Norway was studied by analysis of stomach contents. Temporal variations throughout the winter 1989-1990 and sex and age specific differences in food choice were given special attention. A total of 1,864 food items were found in the 477 stomachs with contents. Otoliths and other fish remains constituted nearly 90% of the items, while 10% were remains of polychaete worms. Clupeids, gadids and gobids were the most common fish groups, both numerically and by frequency of occurrence. Although there were no sex and age specific differences in the frequencies of occurrence of the main prey groups, such differences were evident when data were expressed numerically. Immatures took more clupeids, gobids and polychaetes but fewer gadids than did adults. Males took more clupeids, gadids and polychaetes than did females; females took more gobids than did males. The frequency of occurrence of clupeids, gadids and gobids in adults and immatures showed no significant variation during the winter. There was, however, a significant seasonal variation in the numerical occurrence of gadid items, but not of clupeid items, in stomachs from adults andjuveniles during the three two-month periods in the winter 1989-1990. If this diet was representative, the total food consumption by Common Murres in Skagerrak during October 1989-March 1990 was about 12,520 metric tons, of which clupeids constituted 5,770 tons, gadids 6,435 tons, gobids 50 tons, and polychaetes 63 tons. The consumption of both clupeids and gadids totalled approximately 10% of the total landings by commercial fisheries in the North Sea and Skagerrak areas. Received 1 7June 1998, accepted 21 September 1998.