Fishing Size Rules and Natural Selection

We may be breeding smaller, slower growing, timider fish. [Link]

Rules that allow only the catching of larger fish may encourage their replacement with slower growing, more timid varieties. That, at least, is the concern of researchers who studied test populations in two artificial lakes and report their findings in this week's edition of Proceedings of the National Academy of Sciences.

Peter A. Biro of the department of environmental science at the University of Technology in Sydney, Australia, explained that it's the fast-growing more aggressive fish that tend to get caught, removing them from the breeding pool.

That leaves reproduction up to slower-growing fish who are more timid, he explained in an interview via e-mail.

"This will cause evolution to slower growth rates and slow the rate of recovery for fished populations, and could explain why fisheries tend not to rebound in the manner we expect after we reduce harvest or close a fishery," he said.

"What surprised me was how fast it occurred," Biro said. He said the largest catch occurred on the first day of fishing.

Biro and his colleague, John R. Post, stocked two lakes in western Canada with different types of rainbow trout - one type was known to be aggressive in seeking food and to grow rapidly, while the other grew more slowly and tended to take fewer risks in foraging.

They set gillnets in the ponds over five days, moving them each day, and caught 50 percent of the stocked fast-growing fish but just 30 percent of the more cautious ones.