Los Farallones

Dispatches from Point Blue’s field station on the Farallon Islands National Wildlife Refuge

Goodbye West End, Until Next Year


Last week we took our last visit to West End Island for the season and, as always, it was amazing to see all the pinnipeds basking in the sun and playing in the surf.

Unlike the Southeast Farallon Island (SEFI) which has some human infrastructure, West End Island (WEI) is a specially designated wilderness area, and we are technically visitors when we go to our neighboring island. WEI is separated from SEFI by the Jordan Channel, a sliver of water about 50 feet wide.

The purpose of our visits to WEI is two-fold, to resight flipper tags, and to get a general census of all pinnipeds seen. Flipper tags are usually made of a rubber material in different colors or metal and contain a simple alpha-numeric code which we read through our scopes or cameras.

These observations are sent to NOAA who maintain a large dataset of pinniped tag sightings. This can be used to look at individual pinniped movement and survivorship, as well as general population trends.

In order to limit any disturbance to seabird breeding, WEI is only accessible when seabirds such as Brandt’s Cormorants are not nesting. This short window from mid-September through mid-March is our opportunity to get the most accurate counts of Northern Fur Seals (Callorhinus ursinus) and their pups.

Fur seals are predominantly only seen on WEI and are counted from the lighthouse during weekly island-wide pinniped censuses, but fur seal numbers are more accurately counted from actually visiting WEI. There is such a discrepancy between the lighthouse and on-the-ground counts that a correction factor was developed to better estimate the number of fur seal pups present during the times that we cannot access WEI.

This graph displays lighthouse counts versus an estimate of true numbers using this correction factor. As of the end of the 2020 breeding season we had an estimated record number of over 2,000 fur seal pups on WEI.

We would not be able to conduct this research on WEI if it were not for the permission from USFWS, and we would like to give special thanks to Tony Orr and NOAA for providing us with new equipment to help us with our tag resight efforts on SEFI and WEI. We are very grateful for the cooperative partnerships we have with other agencies and organizations, which are vital to conduct effective research on the Farallones.