Autumn diet of harbour seals (Phoca vitulina) at Prins Karls Forland, Svalbard, assessed via scat and fatty-acid analyses Signe M. Andersen, Christian Lydersen, Otto Grahl-Nielsen, and Kit M. Kovacs Abstract: This study used hard-part analyses from scats (n = 117) and stomachs (n = 3) to investigate the diet of high Arctic harbour seals (Phoca vitulina L., 1758) living on Prins Karls Forland, Svalbard, in early autumn. Additionally, it compared the results of fatty-acid analyses of the seals’ blubber versus that of potential prey with the findings of the more traditional diet assessment method. Svalbard harbour seals appear to be opportunistic, polyphagous feeders similar to the situation in other parts of their range. Members of the cod-family, and secondarily the sculpin-family, dominated the diet of harbour seals on Svalbard. Small fish comprised most of the diet of the harbour seals; invertebrates ap- peared to be insignificant. Atlantic cod (Gadus morhua L., 1758) was the most important species in the diet in terms of biomass, whereas polar cod (Boreogadus saida (Lepechin, 1774)) was the most frequently consumed prey. Our com- parison between hard-part diet analyses and fatty acids is far from definitive, but it indicates a general influence of the diet on the fatty-acid composition of the inner blubber layer. However, it also suggests systematic selective processes in the incorporation of fatty acids into the blubber. Observed differences between the fatty-acid composition of the differ- ent blubber layers and possible differences between sex and age classes warrant further investigation. Résumé : Nous avons analysé les structures dures dans les fèces (n = 117) et les estomacs (n = 3) afin d’étudier le ré- gime alimentaire de phoques veaux marins (Phoca vitulina L., 1758) du haut-arctique vivant à Prins Karls Forland, à Svalbard, au début de l’automne. De plus, nous avons comparé les résultats d’analyses d’acides gras du lard des pho- ques et de leurs proies potentielles avec les résultats des méthodes plus traditionnelles d’évaluation du régime alimen- taire. Les phoques veaux marins de Svalbard semblent être des polyphages opportunistes, comme ailleurs dans leur aire de répartition. Le régime alimentaire des phoques veaux marins de Svalbard est dominé par les poissons de la famille de la morue et secondairement de la famille du chabot. Le régime des phoques comprend surtout des poissons de petite taille; l’importance des invertébrés est insignifiante. La morue franche (Gadus morhua L., 1758) est l’espèce la plus importante en ce qui a trait à la biomasse, alors que le saïda franc (Boreogadus saida (Lepechin, 1774)) est la proie la plus fréquemment consommée. Notre comparaison de l’analyse des structures dures et de l’analyse des acides gras est loin d’être définitive, mais elle montre une influence générale du régime alimentaire sur la composition en acides gras de la couche interne de lard. Elle indique aussi, cependant, l’existence de processus sélectifs systématiques dans l’incorporation des acides gras dans le lard. Les différences observées dans la composition en acides gras des différen- tes couches de lard et les différences possibles entre les sexes et les différentes classeâge requièrent des études supplé- mentaires. [Traduit par la Rédaction] Andersen et al. 1245 Introduction Harbour seals (Phoca vitulina L., 1758) are a broadly dis- tributed pinniped species that occurs throughout much of the northern hemisphere (Bigg 1981). The northernmost popula- tion of this species occurs at Prins Karls Forland, Svalbard. Their occurrence and breeding at this High Arctic archipel- ago is somewhat surprising given that harbour seals are gen- erally a north-temperate species. Foraging studies have been conducted throughout much of the range of harbour seals, but the diet of harbour seals living on Svalbard is currently totally unknown. Harbour seals are known to be shallow divers (Bowen et al. 1999; Lesage et al. 1999; Gjertz et al. 2001; Krafft et al. 2002) that feed opportunistically on a wide variety of fish species, as well as some cephalopods and crustaceans. Dom- inant prey types vary regionally (e.g., Bigg 1981; Bowen and Harrison 1996; Härkönen 1987; Olsen and Bjørge 1995; Tollit et al. 1998) and seasonally (e.g., Pierce et al. 1991; Tollit and Thompson 1996; Brown and Pierce 1998; Hall et al. 1998), as well as interannually (Tollit and Thompson 1996). Harbour seal diet studies considered in combination Can. J. Zool. 82: 1230–1245 (2004) doi: 10.1139/Z04-093 © 2004 NRC Canada 1230 Received 14 July 2003. Accepted 12 July 2004. Published on the NRC Research Press Web site at http://cjz.nrc.ca on 12 October 2004. S.M. Andersen. Zoophysiological Laboratory, August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen, Denmark, and University Studies on Svalbard (UNIS), Department of Biology, Box 156, N-9170 Longyearbyen, Svalbard. C. Lydersen and K.M. Kovacs. 1 Norwegian Polar Institute (NPI), Polar Environmental Centre, N-9296 Tromsø, Norway. O. Grahl-Nielsen. University of Bergen, Department of Chemistry, N-5007 Bergen, Norway. 1 Corresponding author (e-mail: Kit.Kovacs@npolar.no).