Diet of northern bottlenose whales inferred from fatty-acid and stable-isotope analyses of biopsy samples

Abstract

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...

You are what you eat: describing the foraging ecology of southern elephant seals (Mirounga leonina) using blubber fatty acids

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“…Differences in FA signatures among populations, geographical regions and seasons have all been identified (Iverson et al 1997a;Walton et al 2000;Lea et al 2002;Walton & Pomeroy 2003), demonstrating that the technique can be used to detect changes in diet. However, only Iverson et al (1997b) and Hooker et al (2001) have been able to attribute some of these differences to specific prey. Further, no study has determined the spatial and temporal variation in diet structure of individuals relative to foraging regions.…”

Diet of long-beaked common dolphin (Delphinus capensis) in the East Sea, Korea

“…The traditional method of performing a diet study is a stomach content analysis (SCA), which allows a direct observation of prey. However, this method has provided limited information that only shows a representative of recent meals, owing to the inherent delay between feeding and a by-catch event (Hooker et al 2001). Otoliths and beaks can be used to identify prey items in the case of severely digested stomach contents, because these tissues are relatively resistant to digestion and the morphological features of these are species-specific (Harkonen 1986).…”

“…Recently, the analysis of fatty acids (FAs) as a dietary tracer has increased in cetacean diet studies (Hooker et al 2001). FA analysis for dietary study is based on the principle that the FA composition of prey will match that of the predator (Iverson 1993;Budge et al 2006).…”

Evaluation of two underwater biopsy probes for in situ collection of shark tissue samples

“…These involve the firing of stainless steel darts to retain a plug of skin and blubber (Aguilar & Nadal 1984, Barrett-Lennard et al 1996. Researchers approach the target animal on boats, firing the darts with crossbows (Hooker et al 2001), above-water spearguns (Borrell et al 2004) or modified rifles (Krützen et al 2002) ABSTRACT: The design and practicality of underwater biopsy probes was investigated for the in situ collection of shark tissue for molecular analysis. Two probe designs were tested, differing in the structure of their penetrating barrel.…”