Sperm whale diet in New Zealand
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Stomach contents of 19 mature sperm whales, 18 males and one female, that stranded on New Zealand beaches between the mid 1990s and 2004 were examined, identified and measured. Three of the stomachs were empty. All other samples consisted almost entirely of cephalopod beaks. A total of 23,223 cephalopod beaks (10,647 upper and 12,576 lower), representing at least 36 species in 17 families were found in the remaining 16 stomachs. Non-cephalopod remains in the stomachs of sperm whales stranded in New Zealand included limited quantities of fish, salps, crustacean exoskeletons, a copepod, some wood and sand.The present investigation represents the most comprehensive study of the diet of sperm whales in New Zealand since the early 1960s. The results show that oceanic squid of the families Histioteuthidae, Cranchiidae, Onychoteuthidae and Octopoteuthidae are the most common remains found in the stomachs of sperm whales stranded on New Zealand beaches, with the families Onychoteuthidae, Histioteuthidae, Octopoteuthidae and Architeuthidae being the most important by estimated weight in whale diet, and the families Cranchiidae, Pholidoteuthidae and Ancistrocheiridae secondarily so.The beaks of three cephalopod species thought to be restricted to Antarctic waters (Kondakovia longimana, Mesonychoteuthis hamiltoni and Psychroteuthis glacialis) were found in 12 of the stomachs, suggesting these whales had recently migrated into New Zealand from more southern feeding grounds. The amount of local cephalopod beaks in the stomachs suggests some of the stranded sperm whales did not feed much within New Zealand waters in the days prior to stranding.The beaks of Taningia danae, Octopoteuthis megaptera, Octopoteuthis sp. 'Giant' and Lepidoteuthis grimaldii are illustrated and described. Oblique and lateral illustrations of the lower beaks are given, as well as sections of the rostrum, jaw angle, shoulder and lateral wall, to show the major identifying features for each of the species.Squid are an important component of food chains in the Southern Ocean and they act as both high-level predators and prey for apex predators. Therefore, seasonal fluctuations in their abundance must have cascading effects on the diets of apex predators. With increasing global fishing effort, and with cephalopods representing over 4% of the global annual catch, there are competing interests between the ocean's top teuthophagous predators and the fishing industry.Uncertainty of the effects fisheries have on the marine ecosystem has stimulated numerous research studies in recent years. However, despite the economic and ecological importance of cephalopods, there are few ecological studies on them or their significance in the trophic systems of the deep-sea and their life cycles and distribution patterns are only now beginning to be understood. Additional dietary studies that investigate the cephalopod composition and size-class structure in the diet of predators are needed to assess their importance in deepsea food webs, and the potential impact that deep-sea fisheries might have on associated and dependant species, namely apex oceanic predators.The results of this study provide the first significant insight into the diet of the sperm whale, one of the most important apex predators in New Zealand waters.