Yahoo News 17 Apr 08;
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)
Over-fished species go into evolutionary overdrive: study
Yahoo News 16 Apr 08;
Relentless commercial fishing can trigger rapid evolutionary changes when only smaller, younger fish are left behind, a study released Wednesday shows.
Moreover, those changes among fish populations -- a desperate bid to adapt -- may be difficult or impossible to reverse.
Boom-and-bust cycles in over-fished species can wreak economic havoc on fishing communities, and can trigger a downward spiral toward extinction.
The study, experts say, could provide important clues on how to restore fish populations that have, in many cases, been reduced by 90 percent due to decades of industrial-scale fishing.
Scientists have long puzzled over the fact that populations of heavily harvested fish, from sardines to tuna, fluctuate in size more erratically than species that are not plucked from the sea for food.
To find out why, a team of researchers led by George Sugihara at the University of California in San Diego poured over a rare set of data tracking both fished and unfished species off the coast of California over a period of five decades.
In considering three possible explanations, they found no evidence for the first: that fluctuations in population simply mirrored the intensity of commercial fishing.
They did find that the young fish left behind as too small to bring to market were somewhat more vulnerable to the vagaries of the sea, whether changing sea surface temperatures, currents or winds.
The critical factor, however, was not the impact of environmental conditions on these age-imbalanced populations, but an intrinsic lack of stability caused by such "juvenescence," as scientists call it.
The disappearance of older, bigger fish from the population induced early maturation in the survivors in two ways, the study found.
In some cases the smaller fish actually adapted physically to new conditions, changes that could be reversed.
But the researchers also found evidence for a genetic impact, adding weight to a recent body of evidence suggesting that environmentally-driven evolutionary changes can occur far more quickly than once believed.
"The implication is that fisheries management need to give priority to precautionary measures," said Nils Stenseth and Tristan Rouyer, both from the University of Oslo, in a commentary, also published in Nature.
"When the ecological effects of fishing a particular population are observed, the evolutionary consequences may have already set it, and may be irreversible."
