Technological advances are threatening the existence of long-living, deep-sea fish that are already at risk due to overfishing, a U.S. scientist says.

"The harvest of deep-sea fishes is a lot like the harvest of old-growth timber except we don't replant the fish," Selina Heppell, a fisheries biologist at Oregon State University in Corvallis, Ore., said at a weekend meeting of the American Association for the Advancement of Science in San Francisco.

"We have to depend on the fish to replenish themselves. And the habitat that used to provide them protection — the deep ocean — is now accessible to fishing because of new technologies."

Technological advances such as "flash freezing" refrigeration, tracking through global positioning system (GPS) fish-finding and tracking devices and powerful ships that can drag giant nets deep in the ocean make it possible for commercial operations to harvest fish for days at a time.

Most of the fish deemed to be at risk live in international waters, where there are no legal protections to prevent them from being harvested.

Deep-sea species such as orange roughy, the Patagonian toothfish — commonly called Chilean sea bass — and the sablefish, also known as black cod, are among the fish threatened by the new technologies.

Deep-sea fish grow slowly and many don't reach sexual maturity for 30 or 40 years due to limited food sources and slower metabolisms, and don't necessarily breed every year.

Harvesting these older fish could result in further depletion of the fish stocks because they are more likely to breed successfully than their younger counterparts.

"When you buy orange roughy at the store, you are probably purchasing a filet from a fish that is at least 50 years old," Heppell said.

"Most people don't think of the implications of that. Perhaps we need a guideline that says we shouldn't eat fish that are as old as our grandmothers."