Fishing methods affecting evolution of fishes: producing smaller and less fertile fish

Evolution Impact Key to Save Fish Stocks - Scientists
PlanetArk 23 Nov 07

VIENNA - Industrial-scale fisheries have not only sapped the world's fish stocks but also changed the species' evolutionary course, exacerbating the effect of overfishing by producing smaller and less fertile fish.

Scientist Ulf Dieckmann also said that overfishing and the practice of throwing lower quality fish back into the sea to raise the value of fishing quotas might explain the massive drop in population.

"Human activity had a possibly irreversible evolutionary effect in just a few generations," said Dieckmann, a member of a group of scientists who wrote a comment in the journal Science on managing fish stocks published on Thursday.

"We are running up a Darwinian debt that future generations will have to pay back."

Some 15 years ago, cod stocks in the Canadian Grand Banks in the north-west Atlantic collapsed, bringing down the fishing industry in the region. The same species is now under threat in the north-east Atlantic off Norway and Russia, he said.

In the Canadian Grand Banks fish stocks still show little sign of recovery, Dieckmann said, adding that evidence suggested humans were also responsible for this.

Looking at fishery data from the past few decades, the scientists found that increased mortality due to overfishing had favoured fish that matured smaller and earlier, yet also carried far fewer eggs at their first reproduction.

Older data showed that a typical cod caught in Norway might have taken ten years to mature, while the same fish now would only take six years or even less, said Dieckmann.

"The question is not whether such evolution will occur, but how fast fishing practices bring about evolutionary changes and what the consequences will be," scientists wrote in their comment in Science, warning that such evolution may even be irreversible.

Dieckmann expected that a change coming about in 40 years might take up to 250 years to reverse -- if it happened at all.

"Upsetting the dynamics of predators and prey may cause other changes that block this," he said.

Assessing the evolutionary impact could become an essential tool in managing fish stocks, said Dieckmann.

Fishing policymakers could have helped avoid the collapse of cod stocks in the Atlantic by taking into account the fishing industry's impact on evolution in the oceans, and that might help prevent future catastrophes.

Dieckmann said recommendations for future fishing policy based on the research included: less fishing overall; avoiding catching small fish by using wider-meshed nets; and banning fishing in areas where fish spawn.

"Based on data that were available 7-10 years before the collapse of the Grand Banks cod fisheries, an evolutionary impact assessment could have been used to send an early warning signal to policy makers," said Dieckmann.

"(Such assessments) applied now can thus help us avoid future catastrophes unfolding elsewhere," he added. (Reporting by Karin Strohecker; Editing by Elisabeth O'Leary)