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Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

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Abstract:

Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

Nous comparons les patterns de présence de la mère auprès des petits chez l'otarie de Steller (Eumetopias jubatus) en Alaska durant les saisons de reproduction d'été de 1994 et 1995 à l'île Sugarloaf (une population en déclin) et à l'île Lowrie (une population stable). Le but de notre étude est de déterminer s'il y a des différences dans la présence maternelle entre les deux populations qui s'accordent avec l'hypothèse selon laquelle les otaries de Steller nourricières dans les zones de déclin sont limitées par la nourriture en été. Nos attentes a priori sont fondées sur les réactions comportementales bien connues des otaries à la réduction de la disponibilité des proies. Contrairement à nos prévisions initiales, les sorties de recherche de nourriture sont plus courtes dans les zones de déclin; leur durée moyenne est de 19,5 h, par comparaison à 24,9 h chez la population stable. En revanche, la durée moyenne de la période périnatale (entre la mise bas et la première sortie de quête de nourriture) est significativement plus longue dans la zone de déclin (9,9 jours au lieu de 7,9 jours), encore à l'encontre de nos prévisions. La durée moyenne des visites au littoral chez la population en déclin est aussi significativement plus longue (27,0 h par comparaison à 22,6 h chez la population stable). Chez les deux populations, le temps moyen consacré par les mères à la recherche de la nourriture augmente avec l'âge des petits, alors que le temps passé au littoral en compagnie de leurs petits diminue. Ces observations sur le comportement de présence maternelle ne s'accordent pas avec l'hypothèse selon laquelle les otaries de Steller nourricières dans la population en déclin ont du mal à obtenir des proies durant l'été.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2003

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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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