Turbo-evolution shows cod speeding to extinction

Debora MacKenzie, New Scientist 27 May 09;

Fishing is causing cod to evolve faster than anyone had suspected it could, fisheries scientists in Iceland have discovered. This turbo-evolution may be why the world's biggest cod fishery, the Grand Banks of Newfoundland, crashed in 1992 and has yet to recover.

The Icelandic cod fishery, almost the only large cod fishery left anywhere in the world, is about to go the same way unless urgent conservation measures are applied, the scientists warn.

Einar Árnason's lab at the University of Iceland in Reykjavik is part of MADFish, a network of Nordic scientists studying molecular mechanisms of adaptation in fish. They have discovered a gene in cod, Pan I, that seems to govern the depth at which the fish live.

Cod with the B form of Pan I live deeper down, except when they are on the shallow spawning grounds. Cod with the A form of the gene spend all their time closer to the surface.

As the cod close to the surface are most likely to get caught, survival chances of fish with the A gene are only 8 per cent of those with the B gene. As a result, fish with the A gene are disappearing rapidly.
Rapid change

Fisheries are known to exert selective pressure on fish. In some cases this has led to the evolution of smaller fish.

This was thought to be a slow process. "Previous workers have concluded that evolutionary changes are only observable on a longer timescale, of decades," Árnason says. "The changes we observe are much more rapid."

The A gene is being driven out simply because of where those fish choose to live, says Árnason. Such inadvertent, rapid selective pressure may drive some fisheries to crash.

"Man the hunter has become a mechanised techno-beast," the team writes. "Modern fisheries are uncontrolled experiments in evolution."

Worryingly, the researchers found that cod in the Icelandic fishery are becoming sexually mature while still smaller and younger. Something similar occurred in Newfoundland cod just before that fishery crashed. "We think this too is an evolutionary response to the selective pressure of fisheries," says Árnason.

To relieve the pressure, the team recommends setting aside large marine reserves to be kept off-limits to fishing. Spawn from those areas could then replace fish with A genes lost elsewhere off Iceland.

Journal reference: PLoS ONE, vol 4, e5529