On the variation in size and composition of minke whale (Balaenoptera acutorostrata) forestomach contents

Abstract

Forestomach contents from 223 Northeast Atlantic minke whales (Balaenoptera acutorostrata), caught in scientific whaling operations in Norwegian and adjacent waters in 1992-94, were analysed with reference to the feeding behaviour of the species. More than half of the examined forestomachs had single-prey contents. This was particularly evidence for krill (Thysanoessa spp.), herring (Clupea harengus) and capelin (Mallotus villosus), while a more frequent occurrence of gadoid species in mixed-prey forestomachs indicated that there were either less common in single-species aggregations or that they may have occasionally been eaten while pursuing the same prey as the minke whales. Within a given area, it appeared that small and large minke whales exploit the same resources, the forestomachs of the larger animals containing larger food quanta than those of smaller ones. Substantial variations in observed weights of forestomach contents suggest that minke whales usually feed during long and well defined feeding bouts separated by non-feediing periods. Krill was, however, usually found in stomachs with little contents suggesting that it may be consumed during shorter and more frequent feeding bouts. That krill was more dispersed in the area than any of the other prey items may have contributed to this. The available data may indicate that the feeding activity of minke whales is low during late night and early morning.