Modeling haul-out behavior of walruses in Bering Sea ice

Abstract

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]

Bioenergetics model for estimating food requirements of female Pacific walruses Odobenus rosmarus divergens

“…Our model estimates daily caloric demands of 0 to 12 yr old female Pacific walruses based on massspecific metabolic costs associated with their haulout activity budgets (Udevitz et al 2009) and life history stages (Fay 1982(Fay , 1985. Because female walruses achieve full body size at age 12 (Fay 1982), the calo ric demands for females >12 yr were assumed to be equivalent to those of 12 yr olds.…”

Estimates of Minimum Population Size for Walrus near Southeast Baffin Island, Nunavut

“…Haulout duration was longer, about 18 h in August near eastern Ellesmere Island ) than in Alaska in April (about 9 h, Udevitz et al 2009). Applying the long-term mean of 25% to a 24 h period creates an apparent paradox: on average a walrus would be hauled out 6-7 h per day (25-30%) on land, for an average duration of 20-40 h. This contradiction arises because average tag data represent all weather conditions, some of which are not conducive to hauling out or surveys (Olesiuk et al 1990, Udevitz et al 2009). Once a walrus is hauled out and available to be counted, it is likely to remain hauled out and available for the entire survey day.…”

“…As at Svalbard where the average duration of a haulout bouts were 20-30 h (Gjertz et al 2001, Lydersen et al 2008, haulout bouts average 11 h on ice and 38 h on land in Northeast Greenland (Born and Knutsen 1997). The amount of time hauled out on ice is less than on land: about 15% of the sampling time, with durations of 9 h (Udevitz et al 2009). Haulout duration was longer, about 18 h in August near eastern Ellesmere Island ) than in Alaska in April (about 9 h, Udevitz et al 2009).…”

“…The amount of time hauled out on ice is less than on land: about 15% of the sampling time, with durations of 9 h (Udevitz et al 2009). Haulout duration was longer, about 18 h in August near eastern Ellesmere Island ) than in Alaska in April (about 9 h, Udevitz et al 2009). Applying the long-term mean of 25% to a 24 h period creates an apparent paradox: on average a walrus would be hauled out 6-7 h per day (25-30%) on land, for an average duration of 20-40 h. This contradiction arises because average tag data represent all weather conditions, some of which are not conducive to hauling out or surveys (Olesiuk et al 1990, Udevitz et al 2009).…”

“…Once a walrus is hauled out and available to be counted, it is likely to remain hauled out and available for the entire survey day. And, because walrus tend to haul out when other walruses haul out (Fay and Ray 1968, Salter 1979, Born and Knutsen 1997, Lydersen et al 2008, Udevitz et al 2009), their average probability of being counted is not well represented by their longer term average of time hauled out. Instead we used the percentage of time spent 'dry' in the 12 hours immediately preceding our survey (0.42 SD = 0.07, Table 3b) as a proxy for the proportion of walrus hauled out.…”