Linking northern fur seal dive behavior to environmental variables in the eastern Bering Sea

Ruth Joy,Richard D Routledge,Michael G Dowd,Brian C Battaile,Andrew W Trites,Pamela M Lestenkof,Jeremy T Sterling

doi:10.1890/es14-00314.1

Abstract

Northern fur seals (Callorhinus ursinus) breeding on the Pribilof Islands, Alaska have declined dramatically over the past 40 years. Effective conservation of northern fur seals depends on understanding the foraging behavior of adult females whose foraging success is linked to pup survival. We determined the foraging behavior for 11 tagged lactating female northern fur seals from the Pribilof Islands using a state‐space modeling approach with an autoregressive movement model. To interpret at‐sea behavior in the context of oceanic habitat, we spatially and temporally matched high‐resolution reconstructed tracks to a set of environmental covariates that included: commercial groundfish catch, sea surface temperature, primary productivity, wind speed, depth and time of day. We used a Bayesian hierarchical framework to implement a multinomial regression model to link behavior to environmental covariates and account for the mismatch of scale between fur seal behavior and the environmental variables by incorporating an error‐in‐covariates approach into the hierarchical model. The Bayesian framework allowed us to build a single model to synthesize the information from all the northern fur seal foraging tracks and the available information about the underlying environmental conditions. Application of the approach indicated that the behavioral states for the northern fur seal were significantly related to the Alaska commercial groundfish catch, particularly walleye pollock (Gadus chalogramma).

Highlights

The population of northern fur seals (NFS) in the Pribilof Islands of Alaska has declined dramatically during the past 40 years, and continues to decline without any obvious reason yet identified (Towell et al 2006, Lee et al 2014, Towell et al 2014)
This study examined the at-sea foraging behavior of a population of lactating northern fur seals on St Paul Island, Alaska
Information on fur seal behavior was obtained from electronic tags for 11 complete foraging trips

Summary

INTRODUCTION

The population of northern fur seals (NFS) in the Pribilof Islands of Alaska has declined dramatically during the past 40 years, and continues to decline without any obvious reason yet identified (Towell et al 2006, Lee et al 2014, Towell et al 2014). We examined a set of lactating northern fur seals that were tagged on the Pribilof Islands in the Bering Sea during the breeding season of 2005 and 2006 in order to link foraging behavior to environmental conditions and prey fields. Direct information on prey fields is difficult to collect and is not always available This is true for other environmental variables that affect foraging such as bathymetry (Antonelis et al 1997, Call et al 2008) and the shelf break (Goebel et al 1991, Robson et al 2004, Sterling and Ream 2004), lunar cycle (Ream et al 2005), thermocline depth, and surface fronts (Nordstrom et al 2013a, Sterling et al 2014). Behavior of northern fur seals at a breeding site (rookery) on the Pribilof Islands, it is important to emphasize that our approach for analyzing animal movement in relation to the environment is adaptable for other populations and species

MATERIALS AND METHODS

RESULTS

Materials and methods

DISCUSSION