Foraging Ecology of Lactating Steller Sea Lions (Eumetopias jubatus) at Lovushki Island, Russia

Abstract

A key objective of the National Marine Fisheries Service recovery plan for Steller sea lions (SSL – Eumetopias jubatus) is to protect critical habitats. Doing so relies in part on knowledge of SSL ecology based on time-depth data, at-sea dive locations and post-trip dietary analyses. I used data from animal-borne video and data recorders (VDRs) attached to lactating SSL at Lovushki Island, Russia to improve our knowledge by: 1) classifying dives based on three-dimensional swim paths and foraging success, 2) quantifying rates at which prey were encountered and consumed, and 3) testing whether a giving up rule, shown to be applicable to phocids, could similarly benefit SSL.

I identified five dive types: shallow and deep foraging dives, opportunistic foraging dives, a group of unique dives with no consistent behaviors, and non-foraging dives. I found that discrimination between foraging and non-foraging dives was possible with time-depth data alone, but relied on the assumption that time spent swimming horizontally between the descent and ascent represented swimming at the seabed. I also concluded that SSL at Lovushki were consuming enough prey to satisfy their estimated nutritional requirements.

To determine if lactating SSL at Lovushki Island could improve foraging success by incorporating a giving up rule into their foraging strategy I: 1) identified how dive duration varied according to foraging success and 2) constructed a simulation model to simulate the foraging behaviors and habitats of SSL. SSL did not appear to employ a giving up rule when foraging. This was supported by simulation results which showed that using a giving up rule may not allow SSL to markedly improve foraging success.

My research provided the first descriptions of the submerged foraging behaviors of SSL derived from three-dimensional swim paths and video recorded observations of foraging success. Results improved our knowledge of how SSL utilize the marine resources available to them and demonstrated the benefits of deploying VDRs on SSL. VDR deployments at other locations would increase the geographic resolution at which protection measures could be designed by improving our ability to identify and protect resources based on local foraging behaviors and success rates.