Walrus Used and Available Resource Units for Northeast Chukchi Sea, 2008-2012

Abstract

Sea ice loss represents a stressor to the Pacific walrus (Odobenus rosmarus divergens), which feeds on benthic macroinvertebrates in the Bering and Chukchi seas. However, no studies have examined the effects of sea ice on foraging walrus space use patterns. Thus, we examined walrus foraging resource selection as a function of proximity to resting substrates and prey biomass with a matched use-availability design. We quantified biomass of 17 benthic taxa, which included amphipods, bivalves, polychaete, sand dollars, tunicates, and sipunculids. We included covariates for distance to sea ice and distance to land, and systematically developed a series of candidate models to examine interactions among benthic prey biomass and resting substrates. We ranked candidate models with Bayesian Information Criterion and made inferences on walrus resource selection based on the top-ranked model. Biomass of the bivalve family Tellinidae, distance to ice, distance to land, and the interaction of distances to ice and land were in the top-ranked model. Standardized model coefficients indicated that distance to ice explained the most variation in walrus foraging resource selection patterns followed by Tellinidae biomass. Distance to land and the interaction of distances to ice and land accounted for similar levels of variation in foraging walrus resource selection. These data represent the used and available resource units with the covariates of distance to land and distance to ice.