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Marine Ecology Progress Series

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MEPS 183:281-294 (1999)  -  doi:10.3354/meps183281

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

M. B. Santos1,*, G. J. Pierce1, P. R. Boyle1, R. J. Reid2, H. M. Ross2, I. A. P. Patterson2, C. C. Kinze3, S. Tougaard4, R. Lick5, U. Piatkowski6, V. Hernández-García7

1Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, UK
2SAC Veterinary Science Division, Drummondhill, Stratherrick Road, Inverness IV2 4JZ, Scotland, UK
3Zoologisk Museum, University Copenhagen, Universitetparken 15, DK-2100 København Ø, Denmark
4The Fisheries and Maritime Museum, Tarphagevej 2, DK-6710 Esbjerg V, Denmark
5Forschungs-und Technologiezentrum Westküste, Universität Kiel, Werftstr. 6, D-25671 Büsum, Germany
6Institut für Meereskunde, Duesternbrooker Weg 20, D-24105 Kiel, Germany
7Departamento de Biología Animal, Universidad de Las Palmas, E-35015 Las Palmas de Gran Canaria, Spain

ABSTRACT: Stomach contents of 17 sperm whales Physeter macrocephalus stranded in Scotland 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 Arctic waters. Other studies indicate that the majority of the whales were apparently healthy. The diet of these whales was found to consist almost entirely of cephalopods, principally squid of the genus Gonatus (hereafter 'Gonatus', but probably G. fabricii, an oceanic species characteristic of Arctic waters). The other prey species identified were also mostly oceanic cephalopods: the squids Histioteuthis bonnellii, Teuthowenia megalops and Todarodes sagittatus and the octopus Haliphron atlanticus. Although these results are consistent with other recent studies in the area based on single stranded whales, they differ from results of work on whales caught during commercial whaling operations in Icelandic waters (1960s to 1980s) in that little evidence of predation on fish was found in the present study. Remains of single individuals of the veined squid Loligo forbesi, the northern octopus Eledone cirrhosa and the saithe Pollachius virens provided the only possible evidence of feeding in the North Sea. We infer that sperm whales do not enter the North Sea to feed. The timing, and large and uniform sizes of the Gonatus 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 the strandings is consistent with the whales having fed on mature squid, possibly spawning concentrations--as has recently been reported for bottlenose whales. Assuming that the diet recorded in this study was representative of sperm whales during the feeding season, as much as 500000 t of Gonatus could be removed by sperm whales in Norwegian waters each year and up to 3 times that figure from the eastern North Atlantic as a whole. Evidence from other studies indicates that Gonatus is an important food resource for a wide range of marine predators in Arctic waters.

KEY WORDS: Feeding ecology · Cetacea · Stranding · Gonatus · Cephalopoda

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