Historic variation in the diet of harp seals (Phoca groenlandica) in the Northwest Atlantic

Abstract

Abstract Background: traditionally, diets of harp seals in the NW Atlantic have been described using the prevalence of prey items in stomachs. This paper uses an alternative method, reconstructed wet weight, and prevalence to provide new data about dietary variation in nearshore and offshore areas. Methods: diet was determined by reconstructing the contents of 3,299 stomachs collected in 1982, 1986 and 1990–1993 in nearshore and offshore locations. Wet weights of prey were derived from measurements of otoliths and squid beaks in the stomachs. Results: annual, geographic and seasonal differences were observed in the diets of seals collected near Laborador, NE, W and S Newfoundland, and in off-shore areas. In nearshore NE Newfoundland there was a drastic shift in diet from a heavy reliance on capelin (Mallotus villosus) in 1982, to polar cod (Boreogadus saida) from 1986 to 1993. Conclusions: while previous studies concluded that capelin was the major prey, reconstructions of stomach contents have revealed that polar cod has been the most important prey in nearshore areas since 1986. In contrast, capelin is the major component in the offshore diet. Atlantic cod represented only a minor part of prey weight consumed in either area since 1982.