The influence of feeding,enrichment, and seasonal context on the behavior of Pacific Walruses (Odobenus rosmarus divergens)

Though some research exists concerning general behavior and activity patterns of Walruses in zoos or aquariums, less is known about how these patterns change in response to various environmental and temporal contexts. This study presents two studies assessing behavioral changes in relation to feeding period, object enrichment (OE), and season in a social group of four Pacific Walruses at the New York Aquarium. Study 1 examined behavior in relation to feeding context (nonfeed, prefeed, postfeed); data were collected over a three‐week period, resulting in 47 observation sessions for each feeding context. Study 2 examined behavior in relation to OE and season; data were collected in two phases resulting in 12 enrichment and 9 no‐enrichment (NE) observation sessions (Phase 1), and 21 enrichment and 18 NE observation sessions (Phase 2). Study 1 showed that after feeding, oral behavior increased while social behavior and total swim frequency decreased. In Study 2, both swim frequency and social behavior were found to interact with OE and phase, while oral behavior remained constant across all conditions. As in the wild, both studies found all animals to be swimming the majority of the time. Though every animal spent much of its swim time engaged in an Individual Swimming Pattern (ISP), both studies showed that the proportion of ISP (in relation to total time swimming) remained stable across all contexts, suggesting a potential functional role of the ISPs. These results are discussed in light of the ongoing debate over the role of stereotypies in welfare assessment. Zoo Biol 29:397–404, 2010. © 2009 Wiley‐Liss, Inc.     

Indication of two Pacific walrus stocks from whole tooth elemental analysis

The Pacific walrus (Odobenus rosmarus divergens) is considered to be a single panmictic population for management purposes. However, studies on population structuring in this species are limited; in part, because portions of the population’s range are often inaccessible. Therefore, alternative and complementary methods for investigating stock structure in the Pacific walrus are of particular interest. We used measures of elemental concentrations in whole tooth sections from ICP-MS in a discriminant analysis to investigate evidence of stock separation between walruses from two of three known breeding areas (S.E. Bering, St Lawrence, and Anadyr Gulf). Elemental compositions of teeth from female and male walruses from the S.E. Bering and St Lawrence breeding areas were significantly different, providing evidence of separate stocks. We also obtained insights into the potential relation of walruses from non-breeding areas to walruses from these breeding groups based on similarities in their dental elemental profiles.     

Temporal association of serum progesterone concentrations and vaginal cytology in walruses (Odobenus rosmarus)

Concentrations of serum estradiol-17β and progesterone were monitored in six female walruses using an enzyme immunoassay. Progesterone concentrations increased from March to May in females aged 6 y or older, and subsequently declined (October). No significant elevation of estradiol-17β concentration was detected before an elevation of progesterone concentration. Vaginal smears from four females were examined with Papanicolaou staining. In all females, most epithelial cells were basophilic intermediate-superficial cells; no color change from basophilic to eosinophilic of the cells was detected. Meanwhile, the percentage of anucleate cells in vaginal smears reached its highest value before the elevation of progesterone concentration, followed by an increase in the percentage of leukocytes. We inferred that the change in populations of anucleate cells and leukocytes in vaginal smears reflected ovarian status and CL formation in female walruses.     

Pacific walrus: Benthic bioturbator of Beringia

The dependency of walruses on sea ice as habitat, the extent of their feeding, their benthic bioturbation and consequent nutrient flux suggest that walruses play a major ecological role in Beringia. This suggestion is supported by several lines of evidence, accumulated during more than three decades of enquiry and leading to the hypothesis that positive feedbacks of walrus feeding strongly influence productivity and ecological function via benthic bioturbation and nutrient flux. Walruses annually consume an estimated 3 million metric tons of benthic biomass. Walrus prey species inhabit patches across the shelf according to sediment type and structure. Side-scan sonar and our calculations indicate that the area affected by walrus feeding is in the order of thousands of square kilometers per year. Annual to long-term walrus bioturbation results in significant, large-scale changes in sediment and biological-community structure, and magnifies nutrient flux from sediment pore water to the water column by about two orders of magnitude over wide areas. The combined effects of walrus feeding must be placed in the context of long-term, regional climate changes and responses. Should sea ice continue to move northward as a result of climate change, the walrus' ecological role could be diminished or lost, the benthic ecosystem could be fundamentally altered and native subsistence hunters would be deprived of important resources.     

Demography of the Pacific walrus (Odobenus rosmarus divergens): 1974–2006

Global climate change may fundamentally alter population dynamics of many species for which baseline population parameter estimates are imprecise or lacking. Historically, the Pacific walrus is thought to have been limited by harvest, but it may become limited by global warming‐induced reductions in sea ice. Loss of sea ice, on which walruses rest between foraging bouts, may reduce access to food, thus lowering vital rates. Rigorous walrus survival rate estimates do not exist, and other population parameter estimates are out of date or have well‐documented bias and imprecision. To provide useful population parameter estimates we developed a Bayesian, hidden process demographic model of walrus population dynamics from 1974 through 2006 that combined annual age‐specific harvest estimates with five population size estimates, six standing age structure estimates, and two reproductive rate estimates. Median density independent natural survival was high for juveniles (0.97) and adults (0.99), and annual density dependent vital rates rose from 0.06 to 0.11 for reproduction, 0.31 to 0.59 for survival of neonatal calves, and 0.39 to 0.85 for survival of older calves, concomitant with a population decline. This integrated population model provides a baseline for estimating changing population dynamics resulting from changing harvests or sea ice.