Sunday, December 07, 2008

Sea Lions on Mirounga Beach

It started when cormorants began nesting on the marine terrace of Sand Flat and Mirounga Beach (the primary northern elephant seal areas on SEFI) in spring and summer 2007. To prevent disturbance to these seabirds, PRBO biologists stopped checking on the northern elephant seals to read tags in this area during seabird breeding season and into the fall. This lack of human presence coincided with the highest counts of California sea lions in the history of the refuge. More than 1,000 California sea lions and 20 threatened Steller sea lions took up residence on Low Arch Terrace, Mirounga Beach, Last Resort, and the Marine Terrace.

It is one of the many success stories of the Farallon Islands: the return of animals to an area once human pressures are removed. Common Murres were once reduced to fewer than 5,000 on these islands, starting with the Farallon Egg Company stealing tens of thousands of murre eggs to feed gold miners in the Sierra Nevada in the mid-1800s followed by decades of disturbance by the lighthouse keepers and their families. Today, 35 years after the Farallon National Wildlife Refuge was established and most human pressures were removed, 180,000 Common Murres breed on SEFI. Northern fur seals are giving birth to their pups once again on West End nearly 100 years after they were extirpated by Yankee and Russian sealers. Today, the California sea lion population is thriving.

The first priority of the U.S. Fish and Wildlife Service and the Farallon Wildlife Refuge is the protection of wildlife. Therefore, the presence of sea lions, especially federally threatened Steller sea lions, on SEFI’s main elephant seal breeding beaches means that PRBO biologists had to modify traditional research protocols. Sea lions here are sensitive to people and easily scared into the water. Thus, instead of walking amongst the elephant seals and stamping them with bleach numbers, we are watching from afar through scopes, reading tags and trying to identify as many individuals as possible by their unique scars. We also census all the age classes twice a day. Although we won’t be able to identify most individual cows, we can still monitor overall reproduction and population size.

It will be a different year for the elephant seal research program. But we can all celebrate in the thriving wildlife populations of the Farallon Islands, one of the most biologically rich marine environments in the world.

1 comment:

Joelle said...

Hi Monica:
Nice talking to you on New Year's Day, and it inspired me to return to the blog. Interesting about the herds of sea lions, and I'm appreciative of continuing the tradition of finding non- disturbing methods of monitoring the seals. And even a bigger thanks for so articulately describing how and why that is done! Miss you guys, and the island critters, but good to know they are in such good hands. Hi to Derek and Sally(s)!
Joelle Buffa, Farallon Manager 1996-2008.