Study finds catch to throwing back small fry

Keep Darwin in mind when you go fishing.

A new look at what happens when you toss the small ones back -- as often required by law -- suggests it's not really wise to select fish by size. Returning wee ones to the water may force the population to downsize, gradually evolving populations of smaller fish.

In other words, if it's only small fish that survive, it's also the small fish that breed, passing on the genetic trait for smallness.

That's the conclusion reached by researchers at the State University of New York at Stony Brook Marine Sciences Research Center, who studied what happens when anglers select for the big ones, tossing the small fry back. Their results were announced in Friday's issue of Science magazine.

The two researchers, marine biologists David Conover and Stephen Munch, a graduate student, concluded that the requirement to throw the small fish back probably needs rethinking. Instead, they said, it may be wise to set up exclusive "no-take" areas where all sizes and all kinds of fish can grow unmolested, making fish populations more natural. Or, it may even be a good idea to let some of the bigger fish go, too.

"It makes common sense that this is true," said Jack Mattice, director of the New York Sea Grant Program, a coastal resources and information group that does research into commercial and sport fishing. "But this is the first time people have sat down, asked how can we test this thing, and then did it.

"That is what's exciting about their work. This takes it beyond anecdotal information," Mattice added. "The question now is how strongly this applies to the wild situation" at sea.

Critic says test limited

Fish biologist Ray Hilborn, at the University of Washington, in Seattle, argued the test at Stony Brook was too limited to force major changes in fisheries management. He told Science that "all they have done is show that fish growth rates are heritable. What they haven't done is see what the impact of this would be on a realistic fishery."

To test their ideas, Conover and Munch reared six populations of the common bait fish, Atlantic silversides, in captivity. The results were direct and dramatic.

"In populations where we harvested the larger fish," Conover said, the remaining small fish "evolved slower growth rates. And by the fourth generation they were producing a biomass that was only half" of what it could have been.