19 February 2007

Deepwater fish under the gun

Associated Press
As catches close to shore decline, commercial fishers are increasingly exploiting unsustainable stocks in the cold and gloom of the deep oceans, according to researchers.
Deepwater fish under the gun

Long-lived deepwater species like this antarctic 'cod' - actually a toothfish - are increasingly imperiled by fishing. Credit: Wikipedia

SAN FRANCISCO: As catches close to shore decline, commercial fishers are increasingly exploiting unsustainable stocks 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 reported on Sunday that overfishing in deep waters is putting at risk the most vulnerable 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 U.S. panel member Elliott Norse, of the Marine Conservation Biology Institute in Bellevue, Washington. “The number of people who want fish is not going down, but the number of fish is.”

“The harvest of deep-sea fishes is a lot like the harvest of old-growth timber,” said Selina Heppell, a fisheries biologist from Oregon State University in Corvallis, “Except we don’t ‘replant’ the fish. 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.”

The shift to fishing at depths of more than 180 metres 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 deepwater fishing occurs around seamounts, extinct volcanoes that rise from the seafloor to within several hundred feet of the surface. Cold, nutrient-rich upwellings around the seamounts bring food up from the abyssal depths, and many species congregate there to find food and mates. This concentration makes them easier to catch, said Norse.

According to panel members, slow growth and reproduction makes deep-living species particularly vulnerable because they are slow to replenish their stocks. Some deepwater species don’t mature until they are 40 years old and may live for 240 years. Long-lived fish usually have low reproductive rates, either because of low breeding success or high mortality. In the case of deep-sea fishes, both scenarios often play out.

While shallow water skipjack tuna may spawn every day in summer, deep-living orange roughy – actually the re-named slimehead fish – spawn only every two years. “When you buy orange roughy at the store, you are probably purchasing a fillet 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.”

Hempell agreed with Norse that congregating together, such as at seamounts, 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 as Chilean sea bass.

Krista Baker of Memorial University in Newfoundland, Canada, reported that about 40 per cent of deep sea species in Canadian waters are either endangered or show significant decline.

She estimated that because of slow reproduction it would take 12 to 90 years for stocks of roughead grenadier fish to recover if fishing were halted, and 13 to 130 years for roundhead grenadiers.

Other species of fish could take even longer to recover, reported the panel members. According to Heppell, “There are models that estimate the recovery time for some rockfish species is at least 200 years … and we still don’t know all of the factors that influence their survival.”

with Oregon State University
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