Squid in the diet of northern fur seals, Callorhinus ursinus, caught in the western and central North Pacific Ocean

Abstract

The stomach contents of 89 northern fur seals ( Callorhinus ursinus) caught in the western and central North Pacific from December to August during the period 1981–1994 were examined. In total 2567 items including 2401 beaks and 166 digested bodies of squid were obtained. Fifteen species from eight families and four species from three families, respectively, were identified from squid beaks and bodies in the stomachs of seals from the western North Pacific and the central North Pacific. Watasenia scintillans was numerically the dominant prey for northern fur seals in the western North Pacific, while Onychoteuthis borealijaponica and Ommastrephes bartramii tended to be important prey in the central North Pacific. Most of the squid prey were estimated to be smaller than 150 mm dorsal mantle length (DML) except two individuals of Moroteuthis loennbergi and 10 individuals of O. bartramii. Mean size of W. scintillans was almost constant from January to April at 42–44 mm DML. This suggests that northern fur seals feed actively on mature females of W. scintillans when they migrate to shallow waters for spawning during winter and early spring in the western North Pacific, off Honshu, Japan.