Fish policies 'ignore evolution'

Captive fish show what might happen in the wild

By Jo Kettlewell BBC News Online

Current fishing regulations need to be rethought because they ignore evolution, according to new research.

The policy to catch only the larger individuals of any given species - in an attempt to protect juveniles - may cause the average adult size of fish to decrease, it is claimed.

This evolutionary change could cause a whole host of problems for fish populations, such as decreased breeding rates and increased predation.

Fishing practices should preserve the natural genetic variation of fish populations rather than selecting only large individuals, say researchers, or we could see a severe decline in numbers.

Good intentions

International alarm is increasing over dwindling fish stocks and our appetite for fish means that many species are being pushed to the brink of extinction, due to commercial over-fishing.

North Sea cod populations, for example, are thought to be nearing collapse and many other species are severely affected.

This elegant experiment has shown what we already thought

Jack Mattice, Stony Brook University, New York

This has lead to a concerted effort worldwide to tackle the problem before it is too late.

But we could be making matters even worse, according to scientists from Stony Brook University in New York, US, who recently completed an extensive study on captive populations of Atlantic silverside.

Government policies concerned with fish management, such as the European Common Fisheries Policy, recommend that smaller fish are left alone.

Opposite effect

The idea is that by saving the small individuals, fishermen are protecting the future generation of fish and thus preserving the species.

Although the intentions are good the methods are misguided, according to David Conover, Stephen Munch and Jack Mattice, of Stony Brook University.

That is because the current regulations do not take the process of evolution into account.

"An elegant experiment [on captive populations of fish] shows how well intentioned management plans that appear to maximise yield may have the opposite effect after accounting for evolutionary dynamics," said Jack Mattice.

An upper size limit

By catching only large individuals and sparing smaller ones, fishermen are imposing a selective force on the species, which favours little fish.

In other words, fish that happen to be a bit on the small side are likely to have more offspring than their larger neighbours because fishermen - in their quest to save youngsters - avoid them.

This means that smaller fish could eventually become more prevalent within the population. And the implications of this are not good.

The authors of the report claim that populations of fish with a smaller average size could have slower growth and breeding rates; and might be at a greater risk of predation.

Ultimately this may reduce the productivity of harvested fish populations, with naturally slow growing species, such as plaice, being worst affected.

'Interesting dialogue'

However, the problem can be avoided, according to the researchers. Firstly, they suggest an upper size limit - as well as a lower size limit - is imposed on fish destined for our dinner tables.

This would mean that only mid range fish are caught. Secondly, there should be areas that are entirely protected, where no fishing occurs at all, to allow the maintenance of natural genetic variation.

Jack Mattice hopes the warning is heeded.

"These results are not unexpected. This neat experiment has shown what many already thought," he told BBC News Online.

"I hope at the very least it generates an interesting dialogue between fisheries and marine ecologists."

The Stony Brook research is published in the journal Science.