WASHINGTON (Reuters) - Commercial and sport fishing destabilizes fish populations by targeting the biggest, oldest fish and leaving younger fish to proliferate too wildly, U.S. researchers said on Wednesday.
They said fisheries should in fact encourage the taking of smaller, younger fish instead of requiring that they be thrown back.
“That type of regulation, which we see in many sport fisheries, is exactly wrong,” George Sugihara of the Scripps Institution of Oceanography at the University of California San Diego said in a statement.
“It’s not the young ones that should be thrown back, but the larger, older fish that should be spared. Not only do the older fish provide stability ... to the population, they provide more and better quality offspring.”
Writing in the journal Nature, Sugihara said that current policies that manage according to biomass targets instead of individual fish size can also destabilize the population.
A single large fish will simply grow a little when it gets more food, or lose a little weight when food is scarce. A population of many young, small fish, however, may explode in number or collapse depending on food availability.
This is especially important to know when trying to rebuild fish stocks, Sugihara said.
“A high harvest target may be set after an especially abundant period when the population may be poised to decline on its own,” he said.
His team analyzed 50 years worth of records of fished and unfished species from a study set up by the California sardine fishery after its collapse in the 1940s.
Nils Stenseth of the University of Oslo said fishing practices that stress taking only the oldest and biggest fish can actually force quick evolutionary changes in the fish populations.
“Many recent studies have provided evidence for this ... effect, and show that the ecological-evolutionary consequences of harvesting can occur at a much faster rate than previously thought,” he wrote in a commentary.
Reporting by Maggie Fox, Editing by Sandra Maler