Science for a Blue Planet

Science for a Blue Planet

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Return of the Fur Seals

By | December 19, 2014

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The return of the northern fur seals is changing the Farallon Islands, says Russ Bradley, senior scientist with Point Blue Conservation Science.

“Imagine tens of thousands of fur seals on the islands again,” he says. “They are aggressive. This could have a historic impact.”

Bradley is referring to the over 1,000 northern fur seals he and his staff documented this past fall on the islands, a National Wildlife Refuge 30 miles west of San Francisco. Russian and American fur traders wiped out the Farallones population over 150 years ago to sell their luxurious pelts, which can be as thick as 300,000 hairs per square inch.

Imagining the jagged rocks that are the Farallon Islands before 1810 means seeing a landscape transformed during the summer breeding season into a writhing mass of northern fur seals, their guttural growls reverberating, their bodies intertwined and heaped upon each other.

Ryan Berger, Farallon program biologist for Point Blue says northern fur seals are unlike other seal species. “They are more like sea lions. They have external ears and a very short snout, and they move upright on long flippers.”

Northern fur seals spend most their days at sea diving for fish, squid and krill or resting on the ocean’s surface on their backs, also called “jug handling,” since they pull their flippers close to keep warm or wave them in the air to cool down.

During the summer breeding season, the seals converge into giant rookeries primarily on the Pribilof and Commander Islands in the Bering Sea and the Channel Islands near Santa Barbara.

It wasn’t until 1996 that the first modern-day fur seal pup was born on the Farallon Islands, after a handful of adults returned a few years before. Since then, the population has grown, almost doubling in the last two years alone.

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A breeding colony of northern fur seals on the Farallon Islands. Photo: Jim Tietz

“It’s just incredible to see this kind of recovery,” says Bradley, who has worked for Point Blue for 14 years, and has spent over 1500 nights on the islands. “In 2002, I was excited to see two and then four fur seals. Now there’s almost a thousand out there.”

The fur seals now inhabit part of the remote wilderness area of West End Island, where Point Blue staff have to zip-line over a small inlet and overlook them from a rocky ridge—or use aerial surveys to complete accurate population counts. Point Blue has provided a day and night presence on the Farallon Islands since 1968 as part of a unique agreement with the U.S. Fish and Wildlife Service.

Bradley sees a possibility of the fur seals moving toward historic population levels in coming decades. This would bring more change to the islands, including displacing other species, like California sea lions and Cassin’s auklets, a seabird of conservation concern.

“The fur seals are already pushing the California sea lions to other parts of the islands,” Bradley says.

During breeding season, the males, often three times the size of the females, stop eating and aggressively guard harems of 40 or more females and their pups. If the Farallones population continues to increase at dramatic rates, they will expand their breeding colonies onto Southeast Farallon Island as well.

This means the resident population of well over 1500 California sea lions may need to find new habitat, along with about 150 elephant seals, whose numbers have decreased on the Farallones in the last decade due to storm events washing out the sandy haul-out sites they prefer. Most affected may be the Cassin’s auklets, small nocturnal ground-nesting seabirds with struggling numbers, partially due to increasing temperatures on the islands.

Point Blue leads a research and monitoring program for the auklets, and may need to recommend management actions to USFWS if low auklet numbers become alarming. However, as Bradley points out, historic records show the islands originally were covered with northern fur seals and hundreds of thousands of common murres. After murres came close to expatriation in the 1900s due to demand for their eggs, they now number over 250,000.

“Our whole purpose is to give the islands back to the wildlife,” Berger says. “This is the best scenario of letting the natural process work.”

The creation of the Farallones National Wildlife Refuge in the 1960s, with two-thirds of the island chain designated a federal wilderness that is not open to the public, can be credited for providing a safe haven for the northern fur seals’ return. And this may become more important as scientists watch the seals’ numbers plummet in the Bering Sea. The population there has decreased by as much as 50 percent in the last 40 years on some islands.

“Recolonization has occurred in a federal wilderness area,” Bradley says. “And this is helping northern fur seal populations overall. We as scientists are here to watch, document and learn as this drama unfolds.”

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Photo: Jim Tietz

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