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The Gully submarine canyon off eastern Canada has been designated a pilot marine protected area largely because of the northern bottlenose whales (Hyperoodon ampullatus) found there. Studies of this species' diet elsewhere in the North Atlantic Ocean have suggested specialization on the deep-sea squid Gonatus fabricii. We found a high proportion of the congener Gonatus steenstrupi in the stomachs of two bottlenose whales stranded in eastern Canada. In 1997, we collected remote biopsy samples from free-ranging bottlenose whales off Nova Scotia; fatty acids were determined from blubber samples and stable isotopes (carbon and nitrogen) from skin samples. Although fatty-acid stratification throughout the depth of the blubber layer was present (determined from blubber samples of stranded animals), the magnitude of stratification was less pronounced than in many other cetaceans, allowing some qualitative inferences to be made from shallow biopsy samples. Fatty-acid patterns and stable-isotope values from whales were compared with those in samples of G. fabricii from the Norwegian Sea. Blubber fatty acid composition was similar in characteristics to that of adult G. fabricii but was markedly distinct from that of juvenile G. fabricii and other recorded prey species. Nitrogen-isotope values implied that bottlenose whales (mean 15.3‰) and adult G. fabricii (mean 13.7‰) occupy high trophic levels. Overall, the results of these techniques concurred in suggesting that squid of the genus Gonatus may form a major part of the diet of bottlenose whales in the Gully.Résumé : Le canyon sousmarin Gully, au large de la côte est du Canada, a été désigné zone protégée en grande partie à cause de la présence des Baleines-à-bec communes (Hyperoodon ampullatus). L'étude du régime alimentaire de cette espèce ailleurs dans le nord de l'Atlantique indique une préférence pour le calmar d'eau profonde Gonatus fabricii. Nous avons constaté la présence d'une forte proportion de Gonatus steenstrupi, une espèce congénère, dans les estomacs de deux baleines échouées dans l'est du Canada. En 1997, nous avons recueilli à distance des biopsies de baleines en nature au large de la Nouvelle-Écosse; les acides gras ont été déterminés dans les échantillons de lard et les isotopes stables (carbone et azote) dans les échantillons de peau. Bien qu'il y ait stratification des acides gras dans toute la couche de lard (déterminée dans des échantillons de lard prélevés sur des baleines échouées), l'importance de la stratification est moins prononcée que chez plusieurs autres cétacés, ce qui permet de faire des suppositions qualitatives à partir des biopsies faites en eau peu profonde. La distribution des acides gras et la valeur des isotopes stables des baleines ont été comparées à celles de G. fabricii prélevés dans la mer de Norvège. La composition en acides gras du lard est semblable par certaines caractéristiques à celle des adultes de G. fabricii, mais est nettement distincte de celle des G. fabricii juvéniles et à celle d'autres espèces de proies. La vale...

Reliable estimates of diets are vital to monitor impacts of sea lion populations on their ecosystems and their interactions with fisheries, and to understand the role of food to animal nutrition and health. Approaches include using (1) prey remnants in stomach contents, spews and scats; (2) prey DNA in scats; (3) fatty acid signatures in blubber; and (4) stable isotope ratios in predator's tissue. Each methodology has particular advantages and limitations, many of which can be assessed and improved through controlled captive feeding trials. Analysis of prey remnants from captive sea lion scats have shown significant variability in digestion between and within prey species, which, coupled with preferential regurgitation and enumeration biases, can confound accurate diet quantification, but does not prevent spatial or temporal comparisons. Correction for partial digestion and use of additional structures besides otoliths can provide reliable prey size estimates. Prey DNA can be consistently isolated from soft remains in scats from captive sea lions, and with further development this approach may allow quantification of diet. Genetic methods can be expensive and representative of only one to two