Stomach contents of sperm whales Physeter macrocephalus stranded in the North Sea 1990-1996

Stomach contents of 17 sperm whales Physeter macrocephalus stranded in Scot land and Denmark during 1990-96 were analysed. All were sub-adult or adult males and stranded between November and March. They had presumably entered the North Sea during their southward migration from feeding grounds in Arct ic waters. Other studies indicate that the majority of the whales were appa rently healthy. The diet of these whales was found to consist almost entire ly of cephalopods, principally squid of the genus Gonatus (hereafter 'Gonat us', but probably G. fabricii, an oceanic species characteristic of Arctic waters). The other prey species identified were also mostly oceanic cephalo pods: the squids Histioteuthis bonnellii, Teuthowenia megalops and Todarode s sagittatus and the octopus Haliphron atlanticus. Although these results a re consistent with other recent studies in the area based on single strande d whales, they differ from results of work on whales caught during commerci al whaling operations in Icelandic waters (1960s to 1980s) in that little e vidence of predation on fish was found in the present study. Remains of sin gle individuals of the veined squid Loligo forbesi, the northern octopus El edone cirrhosa and the saithe Pollachius virens provided the only possible evidence of feeding in the North Sea. We infer that sperm whales do not ent er the North Sea. to feed. The timing, and large and uniform sizes of the G onatus species eaten (most had mantle lengths in the range 195 to 245 mm), as estimated from measurements of the lower beaks, and the seasonality of t he strandings is consistent with the whales having fed on mature squid, pos sibly spawning concentrations-as has recently been reported for bottlenose whales. Assuming that the diet recorded in this study was repre sentative o f sperm whales during the feeding season, as much as 500000 t of Gonatus co uld be removed by sperm whales in Norwegian waters each year and up to 3 ti mes that figure from the eastern North Atlantic as a whole. Evidence from o ther studies indicates that Gonatus is an important food resource for a wid e range of marine predators in Arctic waters.