Diet and food availability for Northeast Atlantic minke whales Balaenoptera acutorostrata

Abstract

Ecological studies of the Northeast Atlantic minke whale (Balaenoptera acutorostra) were carried out during spring (mainly April-May), summer (June-July) and autumn (AugustSeptember) in 1993 and 1994. Four small-type whaling vessels were chartered for operations in four selected subareas in Norwegian and adjacent waters. To ensure random sampling of whales, stringent sampling procedures, where the vessels searched for whales along predetermined transects within each subarea, were applied. Estimates of potential prey abundance were obtained from a review of results from synoptic surveys and from long-term survey series. Samples were obtained from 63 and 70 whales in 1993 and 1994, respectively. Results from forestomach analyses indicate a minke whale diet where fish play a very prominent role during most of the season. Diets varied between both periods and areas. Gadoid fish species dominated the spring diet. In summer and autumn the diet in the northmost areas (Spitsbergen and Bear Island) was primarily characterized by krill Thysanoessa spp., to a much lesser extent by capelin Mallotus villosus. This is consistent with an increase in krill and severe decrease in capelin availability in these areas in 1993 and 1994 compared with previous years. In the coastal areas of North Norway, herring Clupea harengus is the dominant planktivorous fish, and was also the most important food item for the whales both in summer and autumn. To some extent, however, the herring was accompanied by some gadoid species during summer. Whale consumption of 0-group fish was rather limited. Statistical analyses of potential prey preferences indicate a preference for herring and capelin. Given the opportunity to choose, it appears that minke whales will generally favour these two prey species before other actual species such as krill and gadoid fish species.