Northern fur seal food study in Bering Sea using Saildrone

by Carey Kuhn on 26 Aug 2017 Mother fur seals appear to be taking longer feeding trips than they did last year

The Saildrone is now 10 days into its survey of the northern fur seal foraging area and it’s covered more than half of its survey grid. The fur seals have completed between two and five foraging trips, heading out to sea for an average of just over 5.5 days per trip.

Similar to last year, there is a wide variation in the length of trips the females are taking and the distance and direction they are traveling from St. Paul Island. For example, one female is making trips that take only 4.5 days and she is usually feeding less than 200 km from St. Paul Island (pink lines). In contrast, another fur seal has only completed two trips so far because she is traveling on average over 300 km from the island, taking trips that last 8 to 10 days (green lines).

Our plan for this years’ Saildrone survey grid was to repeat the one conducted in 2016, which was based on a historical analysis of multiple years of fur seal tracking data. For 2016, the historical analysis successfully predicted the core area the fur seals would use and our preplanned grid was right on target. This year, the fur seals are using a larger foraging area. So we had to make last minute changes to the fur seal survey grid extending it to the north and east. The new grid plan now covers our target of 80% of the fur seals use area as of early August.

Plans to collect video of feeding seals in a week

In one week my team and I will head back to St. Paul Island to start the video camera deployments. Six fur seals will carry the video cameras for a single foraging trip. This will give us the opportunity to see when the fur seals are feeding and to capture images of the fish they eat. Once the fur seals return from that trip, we’ll recapture the females and their pups to remove all of the tracking instruments. We’ll also weigh each animal to see how successful they were over the tracking period.

Spotted seal hitches a ride on Saildrone

In other excited news, one of the Saildrones that is currently surveying the Arctic (see mission details here) had a visitor a few weeks ago. The onboard cameras captured a young spotted seal that decided to take a rest on the Saildrone as it transited north. You can read more about it on the Follow the Saildrone website. Although I’ve never seen a northern fur seal in the Saildrone cameras, I’m checking the cameras regularly just in case one of them decides they need a break too!

Check back in a few weeks for an update from St. Paul Island on our video camera deployments and instrument recoveries!