Research Projects >Fine Scale Foraging Behavior of Steller Sea Lions and Northern Fur Seals

Fine Scale Foraging Behavior of Steller Sea Lions and Northern Fur Seals Fine scale foraging data will help to identify critical habitat and assess the extent of spatial overlap with commercial fisheries.

Determining where and how pinnipeds feed is one of the most important research activities needed to assess the population decline and recovery of seals and sea lions. Two basic approaches have been applied to date to assess the foraging behavior of pinnipeds. The first records a detailed two-dimensional profile of the time and depth (TDRs) of pinnipeds in the water column, while the second records a histogram of dive depths made between two points in time (PTTs). Each of these technologies has added substantially to our understanding of where and how pinnipeds forage, yet each has inherent limitations in the quality of information they can deliver. Accurately describing foraging behavior of northern fur seals and Steller sea lions is essential for defining critical habitat. It is also necessary for determining whether they are food limited, and the extent to which their foraging distribution overlaps with commercial fishing activity.

Project Outline
Two inter-related studies are being undertaken over two years to more accurately describe foraging behavior.

Northern Fur Seals:
A newly-developed dead reckoning technology will be used to determine foraging behavior of northern fur seals around the Pribilof Islands. Dead reckoning uses the vectors involved in animal movement to reconstruct the traveling routes in 3-dimensions. This new dead-reckoning technology will be used to extend the simple position studies that have been conducted to date on northern fur seals, and determine the various at-sea behaviors that fur seals exhibit (i.e., sleeping, traveling, feeding, etc.) and how these behaviors relate to localities and fishing activities surrounding the Pribilof Islands. Five lactating northern fur seals from St. Paul Island will be equipped with dead-reckoning tags, satellite PTT tags, and VHF tags in July 2005. They will be recaptured in September to recover the electronic devices. Critical summer feeding habitat for northern fur seals will be identified and the spatial overlap between fur seals and commercial fisheries in the eastern Bering Sea will be assessed, thereby testing the null hypothesis that northern fur seal foraging habitat does not overlap with commercial fisheries in the eastern Bering Sea.

Steller Sea Lions: Satellite tags are the only practical means of monitoring the foraging behaviour of marine mammals in remote areas, and have been widely used on Steller sea lions in Alaska. Due to transmission limitations of the ARGOS system, satellite tags provide only summaries of the number of dives that occurred within pre-specified duration and depth categories, grouped over intervals spanning many hours. Steller sea lions will be captured in Georgia Strait and tagged with TDRs , satellite PTTs, and VHF transmitters in November 2005 and February 2006. The goal of this study is to determine the most meaningful and diagnostic features of diving behavior for various prey types and use them to develop sampling algorithms, onboard processing and transmission protocols that will enhance the interpretation of foraging behavior from future PTT deployments given the bottleneck posed by transmitting data via ARGOS.

Principal Investigator:
Andrew W. Trites, University of British Columbia

Collaborating Investigators:
Pamela Lestenkof, University of British Columbia
Nikolai Liebsch, Leibniz Institute of Marine Sciences
Gabrielle Müller, Leibniz Institute of Marine Sciences
Peter F. Olesiuk, Pacific Biological Station
Rolf Ream, National Marine Mammal Laboratory
Tom Gelatt, National Marine Mammal Laboratory

Funding Source:
NOAA and the North Pacific Marine Science Foundation