Feeding strategy and prey selectivity in minke whales (Balaenoptera acutorostrata) foraging in the southern Barents Sea during early summer

Sammendrag

Stomach content samples from 33 minke whales (Balaenoptera acutorostrata), caught during Norwegian commercial whaling between May-June 1998, were collected in four sub-areas in the southern Barents Sea. Simultaneously, a comprehensive resource survey was conducted in order to identify and estimate the abundance of potential prey items for the whales in the four sub-areas. Krill (Thysanoessa sp. and Meganyctphanes norvegica) dominated the diet in all but one sub-area although pelagic fish such as capelin and herring also contributed significantly. The minke whales displayed monophagus feeding in all sub-areas investigated, including the medium-scale area resulting from pooling of all sub-areas. The small-scale resource surveys revealed significant variations in absolute and relative prey abundance between sub-areas, while the temporal (1-7 days) variations in relative prey biomass within sub-areas appeared to be less significant for all prey items, except herring (Clupea harengus) and perhaps capelin (Mallotus villosus). Krill was by far the most important prey item available in all areas, followed by either herring, cod (Gadus morhua) or saithe (Pollachius virens), depending on sub-area and survey. Although minke whale prey preference appeared to vary greatly in space, some new features of minke whale foraging behaviour were evident. Minke whales showed a strong preference for capelin, whereas gadoids (cod, haddock (Melanogrammus aeglefinus) and saithe) appeared to be avoided by the whales. Krill appeared to have been either avoided, fed upon randomly or were the preferred prey depending on sub-area and analyses level.