Geographical and seasonal changes of the prey species of minke whale in the Northwestern Pacific

Abstract

The forestomach contents of 498 minke whales Balaenoptera acutorostrata sampled in the Northwestern Pacific from May to September through the 1994-1999 JARPN surveys, were analysed. Sixteen prey species consisting of 1 copepod, 4 euphausiids, 1 squid, and 10 fishes were identified. The minke whale in the Northwestern Pacific is a swallowing, feeding-type species. It feeds on swarming zooplankton and schooling fishes, suggesting that minke whales pursue single prey-species aggregations. The results showed geographical and seasonal changes of prey species. On the Pacific side of Japan, Japanese anchovy was the most important prey species in May and June, while Pacific saury was most important in July and August. Walleye pollock was also an important prey species during June and September in coastal waters, over the continental shelf. In the southern Okhotsk Sea krill was the most important prey species in July and August. These changes probably reflect changes in the availability of the prey species in these areas. It would seem that there might be direct competition between minke whales and the fishery for Pacific saury. © 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.