Bearded seals are large phocids that inhabit circumpolar Arctic and Sub-Arctic waters. They are benthic feeders, consuming a broad variety of epifaunal and infaunal invertebrates and demersal fishes, primarily at depths < 200 m. Bearded seals and their foraging habitat requirements are poorly documented, yet this information is crucial for assessing the potential future impacts of industrial activities and a warming climate.
Our goals were to locate ecologically important areas and to identify specific factors driving bearded seal habitat selection in the northeastern Chukchi Sea during the largely ice-free period of high productivity from late June to late November.
Instead of merely examining space use, we modeled the foraging movements of bearded seals as a function of specific biological and environmental features (i.e., benthic prey composition and abundance, sediment type and water depth), using a two-stage analysis. In the first stage, we used a multistate movement model to identify benthic foraging activity based on biotelemetry data collected from seven tagged adult and sub-adult bearded seals. In the second stage, we fit point process models for resource selection using benthic prey data (collected using trawls and van Veen grabs) and other environmental covariates as predictors of the benthic foraging locations identified in the first stage.
Results/Conclusions
Bearded seals exhibited positive selection (i.e., preference) for a diverse array of invertebrates (e.g., bivalves and crustaceans) and fishes. For many fish, only the smaller age-classes were selected for, supporting previous observations from stomach samples. In addition, areas of mud or finer sand were selected against (i.e., avoided). These differences are perhaps related to different prey occupying different sediment types or to the difficulties of foraging in finer-grain sediments.
Many of the taxa that were positively selected for have spatial distributions that are concentrated within 50-90 km of the Alaska coastline, a region identified as an ecological hotspot for bearded seal foraging. Indeed, this area appears to constitute a summer “smorgasbord” for these benthic foragers. In contrast, one location farther offshore (71° 20’N 163° 00’W) contained a suite of prey and sediment types that appeared to be avoided by bearded seals. This location is also coincident with high densities of walrus (a competitor with, and predator of, bearded seals), strong currents and significant industrial activity related to oil and gas exploration. Further research will be required, to determine the extent to which these conditions caused bearded seals (or their preferred prey) to avoid the area.