Foraging behaviour of Weddell seals, and its ecological implications

Abstract

Time-depth recorder data of eight adult Weddell seals (Leptonychotes weddellii) provided simultaneous dive records over 8 days in the Drescher Inlet, eastern Weddell Sea coast, in February 1998. The seals primarily foraged within two depth layers, these being from the sea surface to 160 m where temperature and salinity varied considerably, and near the bottom from 340 to 450 m where temperature was lowest and salinity highest. While both pelagic and benthic diving occurred during daylight, the seals foraged almost exclusively in the upper water column at night. Trawling during daytime confirmed that Pleuragramma antarcticum were by far the most abundant fish both in the pelagial and close to the bottom. Pelagic night hauls at 110-170 m depth showed highly variable biomass of P. antarcticum. The temporal changes in the local abundance of P. antarcticum, particularly in the pelagial, may explain the trends in the seals' pelagic and benthic foraging activities. This study describes the jaw movements of a hunting seal, which are presumably indicative of feeding events. Trophic links from the Weddell seal to fish, zooplankton and krill, Euphausia superba, are discussed.