A unique subspecies of fox that is about the size of a house cat is back from the brink of extinction on Santa Catalina Island and can survive on its own thanks to a captive breeding program, the head of a nonprofit group that manages most of the island said Tuesday.

With the release of the remaining foxes in the coming weeks, the program will come to an end, said Ann Muscat, president of the Catalina Island Conservancy.

The conservancy released nine foxes Tuesday, five pups and four adults. The animals quickly scampered into the scrub-covered hills on the eastern end of Catalina.

Santa Catalina Island foxes now number about 300 and will be monitored closely to make sure they don't again drop to a critical level, Muscat said.

"We feel that the population will be able to do well on its own without us doing captive breeding," she said. "We're going to rely on them to breed on their own."

The Santa Catalina fox was nearly wiped out by an outbreak of canine distemper virus, causing the population to drop from about 1,300 in the 1990s to just 100 four years ago.

The conservancy began trapping and vaccinating foxes in 2000 and has released 37 foxes that were bred in captivity.

Catalina, about 25 miles off Los Angeles, is one of the eight Channel Islands. Six of the islands have a distinct subspecies of fox, four of which are listed as endangered.

The Catalina fox, which weighs 5 to 6 pounds, is a smaller, distant relative of the mainland gray fox. Because the animal evolved in the relative isolation of the island, it was especially vulnerable to the canine distemper virus, which biologists suspect came from a pet.