SAN FRANCISCO — With declining catches close to shore, commercial fishing is turning to deeper waters, threatening species that live in the cold and gloom of the deep oceans, according to researchers.

A panel at the annual meeting of the American Association for the Advancement of Science said Sunday that overfishing in deep waters is putting at risk the least sustainable of all fish stocks.

"We're not really fishing there. We're mining there. We're taking what appears to be a renewable resource and turning it into a nonrenewable one," said Elliott Norse of the Marine Conservation Biology Institute in Bellevue, Wash.

"The number of people who want fish is not going down, but the number of fish is," Norse said.

The shift to fishing at depths of more than 600 feet is new. These areas began to be exploited after overfishing caused a decline in catch in more shallow coastal waters, said Norse.

Much of the deep-water fishing occurs around seamounts, extinct volcanoes that rise from the seafloor to within several hundred feet of the surface.

Many species tend to congregate at seamounts because they can find food and mates there — which also makes them easier to catch, said Norse.

Selina Heppell of Oregon State University said slow growth and reproduction make deep-living species particularly vulnerable because they are slow to replenish their stocks.

Some deep species don't mature until they are 40 years old and then may live 240 years, Norse said.

Such fish reproduce slowly, Heppell said — for example while skipjack tuna may spawn every day in summer, deep-living orange roughy spawn only every two years.

Hempell agreed with Norse that congregating together increased their vulnerability and noted these fish are the least monitored and protected in the oceans.

In addition, Heppell said, rising market value of fish has led to marketing campaigns to increase sales, such as renaming the slimehead fish orange roughy and the toothfish Chilean sea bass.

Krista Baker, a graduate student at Memorial University of Newfoundland, reported that about 40 percent of deep-sea species in Canadian waters are either endangered or show significant decline.