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Intraspecific comparison of diet of California sea lions (Zalophus californianus) assessed using fecal and stable isotope analyses

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Abstract:

The diet of juvenile and adult female California sea lions (Zalophus californianus (Lesson, 1828)) at San Miguel Island, California, was estimated and compared using fecal and stable isotope analyses to determine dietary differences by age. Fecal samples were collected during 2002-2006 and prey remains were identified. Stable carbon (13C) and stable nitrogen (15N) isotope values were determined from plasma and fur obtained from yearlings, 2- to 3-year-old juveniles, and adult females during 2005 and 2006. Juveniles ate more than 15 prey taxa, whereas adult females consumed more than 33 taxa. Relative importance of prey was determined using percent frequency of occurrence (%FO). Engraulis mordax Girard, 1854, Sardinops sagax (Jenyns, 1842), Merluccius productus (Ayres, 1855), genus Sebastes Cuvier, 1829, and Loligo opalescens Berry, 1911 were the most frequently occurring (%FO > 10%) prey in the feces of both juvenile and adult female sea lions, although their importance varied between age groups. Only yearlings had significantly different isotopic values than older conspecifics, indicating that older juveniles were feeding at a similar trophic level and in similar habitats as adult females. Whereas each method had biases, combining the two provided a better understanding of the diet of California sea lions and intraspecific differences.

Des analyses fécales et des analyses d’isotopes stables nous ont permis d’estimer le régime alimentaire de jeunes et de femelles adultes du lion de mer de Californie (Zalopus californianus (Lesson, 1828)) à l’île San Miguel, Californie, et de comparer les différences alimentaires en fonction de l’âge. Nous avons prélevé des échantillons de fèces en 2002-2006 et identifié les restes de proies. Nous avons déterminé les valeurs des isotopes stables de carbone (13C) et d’azote (15N) dans le plasma et la fourrure provenant d’individus de l’année, d’individus de 2-3 ans et de femelles adultes en 2005 et 2006. Les jeunes consomment plus de 15 taxons de proies, alors que les femelles adultes en utilisent plus de 33. L’importance relative des proies est représentée par la fréquence d’occurrence en pourcentage (%FO). Engraulis mordax Girard, 1854, Sardinops sagax (Jenyns, 1842), Merluccius productus (Ayres, 1855), le genre Sebastes Cuvier, 1829 et Loligo opalescens Berry, 1911 sont les proies qui apparaissent le plus fréquemment (%FO > 10 %) dans les fèces des jeunes lions de mer et des femelles adultes, bien que leur importance varie selon les groupes d’âge. Seuls les individus de l’année présentent des valeurs isotopiques différentes de celles de leurs congénères plus âgés, ce qui indique que les jeunes plus âgés se nourrissent au même niveau trophique et dans des habitats de même type que les femelles adultes. Bien que chaque méthode ait ses sources d’erreurs, la combinaison des deux permet une meilleure compréhension du régime alimentaire des lions de mer de Californie et de ses différences intraspécifiques.

Document Type: Research Article

Publication date: February 1, 2011

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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