Northern Fur Seals Rebounding in the Farallones

By Stefan Marti
Published: March 2007

Mother and pup fur seal. Credit: NOAA

Two centuries ago, hundreds of thousands of northern fur seals lived, bred and reared their young in the Gulf of the Farallones National Marine Sanctuary.  Then, in the early 1800’s, British, Russian and American hunters discovered their thick luxurious pelts—with over 350,000 hairs per square inch—and within a few decades all of the seals were either slaughtered or had fled.

IIn the early 1970’s, after almost a century and a half absence, a handful of male fur seals returned to the Farallon Islands.  In each of the following years, a few more seals arrived, and in 1996, the first northern fur seal pup was born in the sanctuary in over 150 years.  “It is an amazing sight,” says GFNMS Research Coordinator Jan Roletto, “to see northern fur seals return after so many years.”

Since 1996, the number of births has increased each year, and in 2006 more than a 100 pups were born.  "We're starting to see the beginning of exponential growth," says Carol Keiper, FMSA marine biologist and naturalist.

A probable reason for their rebound in the area is the abundant food supply in the sanctuary waters.  Northern fur seals are voracious hunters, feeding on salmon, pollack, herring and squid.  They spend most of their life at sea, hauling out only to breed and raise their young.  Pups are quickly weaned, joining their parents after a few months in the open waters.

Changing Food Chain

There are a few predators that will welcome the growing population of northern fur seals in the sanctuary.  White sharks and killer whales both feed on fur seals.  And if the fur seal population slowly returns to its original size, there are many species that will have to compete with the new arrivals.  Not only the other seals and sea lions, but many of the sea birds that nest on the islands, such as Cassin's auklets, which have suffered almost complete breeding failures for two consecutive years at the Farallons.

Northern fur seals are found across the northern Pacific—from Japan to Alaska to Baja California—and though their population is growing in the Farallones, their numbers are shrinking rapidly at the Pribilof Islands in Alaska, one of their main breeding grounds.  Many scientists believe the decline is due to over-fishing in the area. 

Fur seals are much larger than their counterpart harbor seals, which also haul out on the Farallon Islands.  Males can weigh up to 600 pounds, while females are much smaller at 60 to110 pounds.  With large, furless, front flippers and rotating back flippers, they can “walk” much like sea lions.  Fur seals also have tightly-rolled ears for good hearing and keen eyesight, which make them great hunters.

Breeding season is in the summer, so if you want to see the blossoming population of northern fur seals on the Farallones, sign up for our whale watching trips in the upcoming months.