Understanding haul-out behavior of ice-associated pinnipeds is essential for designing and interpreting population surveys and for assessing effects of potential changes in their ice environments. We used satellite-linked transmitters to obtain sequential information about location and haul-out state for Pacific walruses, Odobenus rosmarus divergens (Illiger, 1815), in the Bering Sea during April of 2004April of , 2005April of , and 2006. We used these data in a generalized mixed model of haul-out bout durations and a hierarchical Bayesian model of haul-out probabilities to assess factors related to walrus haulout behavior, and provide the first predictive model of walrus haul-out behavior in sea ice habitat. Average haul-out bout duration was 9 h, but durations of haul-out bouts tended to increase with durations of preceding in-water bouts. On average, tagged walruses spent only about 17% of their time hauled out on sea ice. Probability of being hauled out decreased with wind speed, increased with temperature, and followed a diurnal cycle with the highest values in the evening. Our haul-out probability model can be used to estimate the proportion of the population that is unavailable for detection in spring surveys of Pacific walruses on sea ice.Résumé : Il est essentiel de comprendre le comportement d'échouerie chez les pinnipèdes associés aux glaces pour planifier et interpréter les inventaires démographiques et pour évaluer les effets des changements potentiels dans leurs environnements glacials. Nous avons utilisé des émetteurs reliés aux satellites pour obtenir des informations séquentielles sur la position et l'état d'échouerie de morses du Pacifique (Odobenus rosmarus divergens (Illiger, 1815)) dans la mer de Béring en avril 2004de Béring en avril , 2005de Béring en avril et 2006. Ces données utilisées dans un modèle de mélange généralisé de durée des épisodes d'échouerie et un modèle hiérarchique bayésien des probabilités d'échouerie nous servent à évaluer les facteurs reliés aux comportement d'échouerie chez les morses et à mettre au point le premier modèle prédictif sur le comportement d'échouerie chez les morses dans un habitat de glace de mer. Les morses marqués passent en moyenne 9 h par épisode d'échouerie, mais les durées des périodes d'échouerie ont tendance à s'allonger en fonction de la durée des périodes précé-dentes passées en mer. Globalement, les morses marqués passent en moyenne seulement 17 % de leur temps en échouerie sur la glace de mer. La probabilité d'échouerie diminue en fonction de la vitesse du vent, augmente avec la température et suit un cycle journalier avec un maximum en soirée. Notre modèle de probabilité des échoueries peut servir à estimer la proportion de la population qui est à l'abri de la détection lors des inventaires printaniers des morses du Pacifique sur la glace de mer.[Traduit par la Rédaction]

Pacific walruses (Odobenus rosmarus divergens) are harvested by subsistence hunters in Alaska as they migrate north through the Bering Strait in the spring. Harvest records and biological specimens have been collected from the Bering Strait communities of Little Diomede, Gambell, and Savoonga since the 1950s. Harvest levels in the Bering Strait region peaked in the late 1980s and declined thereafter; however, there was considerable variation in the size and composition of the harvests among communities and over time. The relationships among characteristics of the community harvests and the presence of temporal trends were investigated using generalized linear models. The proportion of females in the catch increased over time in all three communities, while the proportion pregnant among harvested females declined over the range of sample years. The ages of harvested walruses increased over time in all three communities through the 1980s, after which trends in age stabilized or began to decline. The age of first reproduction was significantly older for females sampled in 1975-1985 than for females sampled between 1952 and 1962 or 1992 and 1998. Factors thought to have influenced the size and composition of the catch over the past 50 yr include hunter preferences, harvest management regimes, environmental conditions, and changes in the population itself.

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The relationship between the numbers of growth layers counted in the mandible and in the cementum of lower canines from 87 walrus (Odobenus rosmarus rosmarus) was examined. A 1:1 correlation between counts of growth layers in the two tissues was found in males ≤ 19 years old and females ≤ 9 years old. No correlation was found in males with ≥ 21 or in females with ≥ 10 cemental growth layers. In physically mature walrus, mandibular layering was unreliable for age analysis. Resorption and a reduced mandibular growth rate appear to be the main factors limiting mandibular age estimates in mature walrus.