A new paper linking fur seal dive behaviour to prey abundance has recently been published in the journal Ecosphere. Northern fur seals are found in the North Pacific Ocean along the coast of North America from the Baja Peninsula to Alaska, extending west to Japan and Russia. They are currently listed as threatened under the IUCN and the majority of the world’s population lives in the Pribolof Islands of Alaska, which is also the location of an important breeding site. This population has been steadily declining for over 40 years with no known cause. The team lead by Dr. Ruth Joy sought to determine foraging behaviour of Northern fur seals as conservation plans rely heavily on the knowledge of basic animal ecology and especially the foraging success of females with pups.

A group of lactating females were tagged on the Pribilof Islands to determine the relationship between foraging behaviour and environmental variables in the Bering Sea, including the commercial groundfish catch, sea surface temperature, primary productivity, wind speed, ocean depth, and time of day. Using a state space modeling approach to categorize behaviour (i.e., non-diving, active, and exploratory diving), the 3D tracks of 11 complete at-sea tracks were linked to these environmental covariates over different parts of their trips.

Active northern fur seal dive behaviour was strongly associated with areas of high groundfish catch, and in particular, the density of walleye pollock, which is the most common component of their diet. A strong preference was shown for active diving at night. Although this study cannot draw conclusions about the interactions of northern fur seals with commercial fisheries, the results suggest that they are likely reducing their energetic costs by employing different dive strategies while in different areas of the Bering Sea and during different parts of the day – important movement and foraging information necessary for conservation management plans.

Interested in learning more? Read the full paper here.