February 26, 2008

Releasing Smaller Fish Weakens Breeding Pool

According to new research, the catch-and-release rule, which implies keeping larger fish while releasing the smaller ones, could actually be counterproductive.

Peter A. Biro of the department of environmental science at the University of Technology in Sydney, Australia presented the new research in the recent edition of Proceedings of the National Academy of Sciences.

He found that since the larger fish are usually the more aggressive ones, their being caught may lead to a breeding pool full of less powerful, more timid fish.

"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.

His team of researchers studied the effects of fishing and population in two artificial lakes which were stocked with various types of rainbow trout in western Canada. One of they types is known to be a more aggressive fish when it comes to hunting out food, while the other took fewer risks.

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

Gillnets were placed in the ponds over five days, and were moved after each day. The nets brought in 50 percent of the stocked fast-growing fish, while only 30 percent of the more cautious ones were present.

Biro and his colleagues were concerned because generally the more aggressive, energetic fish grow faster and survive.

"Fish that are highly active and bold tend to bump into these nets more often and are less likely to avoid them," he explained. And increased activity is necessary to get enough food for rapid growth.

John Waldman, an aquatic biologist at Queens College in New York, said that the new research shows that mating among stronger, faster fish is "even more important than previously recognized."

"Harvest of fishes is probably the most profound impact mankind is having on the sea, yet we rarely succeed in even the basics of achieving long-term sustainability of important commercial species," said Waldman.

The research was supported by the University of Technology Sydney and the National Science and Engineering Research Council of Canada.


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