Cephalopods as prey. III. Cetaceans

Abstract

Over 80 % of odontocete species and two balaen whale species include cephalopods in their diet regularly. In 28 odontocetes they comprise the main food. Predominently cephalopod-eating species are found in the Physeteridae, Ziphiidae, Phocaenidae and Delphinidae. By far the most important of the 28 families of cephalopods represented in the diet of cetaceans are the oceanic Ommastrephidae, Histioteuthidae and the Cranchiidae, with the neritic Loliginidae assuming most importance on the continental shelves. Onychoteuthidae and Gonatidae assume greater importance in polar regions and the North Pacific. The other 22 families form a reservoir from which various cetaceans eat opportunistically and as their sizes permit. There are probably less than 60 cephalopod species regularly in the diet of cetaceans. Species composition of the food varies regionally, seasonally and annually. Locally, the greatest difference is found between cetaceans that live in oceanic water and continental shelf water. There is a positive correlation between the size of the prey and both the size of pelagic feeding cetacean species and the growth stage within a species. This leads to some partitioning of the food and less competition. Broad estimates show that the biomass of oceanic cephalopods consumed annually by the largest odontocete, Physeter catodon , may be over twice the biomass of fish caught by man. Regional estimates show that consumption by cetaceans of little known cephalopod species may greatly exceed the local catches of commercial fish.