It took commercial hunters less than 40 years to wipe out the valuable seal species on California’s Farallon Islands. In 1807, a sea captain spotted huge colonies of fur seals and elephant seals on the granite outcrops 27 miles off San Francisco’s Golden Gate. By 1840, the colonies were gone—the elephant seals hunted to extirpation for their blubber, the fur seals for their coats.

Forty years after the Marine Mammal Protection Act of 1972 (MMPA) and 38 years after most of the islands’ wilderness designation, northern fur seals and elephant seals are breeding again on Farallon National Wildlife Refuge. The islands, in one of the world’s richest marine upwelling zones, provide important breeding and haul-out habitat for five pinniped species. Twenty-three species of whales, dolphins, sea otters and other marine mammals also swim in the waters.

Globally, marine mammals still face grave threats, from polluted seas, ship strikes and ghost fishing nets to cascading changes in marine ecosystems. But there is good news from refuges, including Farallon.

In 1972, researchers observed the first elephant seal pup born on the Farallon Islands in about 100 years. In 1996, northern fur seals returned to give birth for the first time since the era of wanton commercial hunting. Their population has grown steadily to more than 500 animals. At least 180 northern fur seal pups were born on the islands in 2011.

The northern fur seals’ rebound “is really a tremendous success story,” says Russell Bradley, Farallon program manager for PRBO Conservation Science, an independent research organization that administers the refuge with the Service. “This national wildlife refuge has expanded the range of this species in the Lower 48 states ... That’s pretty significant.”

Northern fur seals were once “the most abundant pinnipeds on the islands,” says Farallon Refuge manager Gerry McChesney. “For 150 years, they were gone. Now, they’re back and they’re continuing to expand.”

McChesney and Bradley credit synergy between the MMPA, which outlawed killing, selling, capturing or harassing marine mammals in the United States, and land and sea protections put in place at about the same time.

They cite the 1965 closure of a U.S. Navy radio station; expansion of Farallon Refuge in 1969 and 1974, with two-thirds of the island chain designated as wilderness; and the 1981 creation of the Gulf of Farallones National Marine Sanctuary, managed by the National Oceanic and Atmospheric Administration (NOAA). Together, these changes gave managers tools to significantly reduce human disturbance of the islands’ wildlife.

Today, the islands’ only human inhabitants are a few biologists and refuge staff. Visitors can explore the islands by boat, at speeds of 5 mph and from a football-field distance most of the year. To prevent stampedes, overflights lower than 2,000 feet are forbidden.

Before the MMPA, rowdy boaters harassed and occasionally shot at the islands’ pinnipeds, but public attitudes have changed and such incidents are rare.

The trends are not all positive. Since the 1980s, El Niño storms have eroded the sandy beaches where elephant seals breed and haul out. In 2011, only 96 elephant seal pups were born on the refuge, the fewest since 1976.

Threatened Steller sea lions are declining throughout the central California portion of their range, victims of contaminants, disease and changes in ocean currents. Very few pups are born on the Farallon Islands.

But observers occasionally see the rarest native pinniped, the Guadalupe fur seal. Hunted almost to extinction, that species now breeds only off Baja California, but its numbers are slowly growing and managers hope it may one day recolonize the Farallones.

Heather Dewar is a writer-editor in the Refuge System Branch of Communications.