Once hunted to the brink of extinction for their luxurious pelts, California’s sea otter population has shown steady growth, although more slowly than predicted, a U.S. Fish and Wildlife study says.

The agency announced Wednesday in its final southern sea otter stock assessment report that the population has grown slowly over the past five years.

The report’s 2008 spring survey count indicates the state’s sea otter population grew 3 percent annually from 2003 to 2007, rather than the predicted 5 percent. The running three-year average from 2006 to 2008 was 2,826 individual otters.

The overall count includes a small colony near San Nicolas Island off the coast of Ventura County. That population, the result of relocation efforts initiated in 1987, is considered to be a “nonessential experimental” under the Endangered Species Act.

The San Nicolas colony numbers about 42, including 37 independent sea otters and 5 dependent pups. The survey found the population has grown by an average of about 9 percent a year since the early 1990s.

“Surveys over the past five years suggest the recovery of the sea otters is continuing,” said Lilian Carswell, the agency’s sea otter coordinator. “It’s a slow upward trend but an upward trend nevertheless, and, as it stands now, that’s a positive sign.”

In the 18th and 19th centuries, otters were hunted throughout their entire habitat range, from Oregon to Baja California. By the early 1900s, only a small remnant colony survived off the Big Sur coast. The species — a key link in the California marine ecosystem — was listed as threatened in 1977 under the Endangered Species Act and was considered a depleted species under the Marine Mammal Act.

In 1914, there were an estimated 50 otters near Bixby Creek in Monterey County. Placed under protection through the International Fur Seal Treaty in 1911, southern sea otters have been able to expand northward and southward along the Central Coast.

The report, developed in accordance with the Marine Mammal Protection Act and available online at http://www.fws.gov/ventura, warns that southern sea otters are still threatened by disease and catastrophic events.

Unanswered in the report because observer programs are not in place is whether otters are being taken in by commercial fisheries. The study indicates a very high level of observation would be needed to find any indication of mortality in fisheries.