Fishing Changes Fish Population

Friday, July 20, 2001 By Associated Press

BREWSTER, Mass. The reason fishermen are catching smaller fish than their predecessors might not be just because all the big ones have been caught.

Research indicates that as bigger fish are removed from the population, the smaller fish left behind take on more influence in breeding the next generation.

"It's like (eliminating) all the people who are 7 feet tall; they will become rarer and rarer and you'll have only small people left. It's fascinating to think humans are having this effect on fish," Steven Murawski, chief of the population dynamic branch of National Marine Fisheries in Woods Hole, told The Boston Globe.

Some of those smaller fish also are reaching sexual maturity earlier, producing offspring that are both small and programmed to be mothers while still young.

In the 1960s, most Boston haddock spawned at age 3 or later, but now even 1-year-olds are spawning. Cod are also having offspring at younger ages. On the West Coast, the average size of pink salmon coming back to spawn decreased 30 percent in 40 years.

Scientists say it is difficult to sort out what is true genetic or evolutionary change and what is a short-term physiological adaptation that will end when fishing pressure does.

If a genetic change is occurring, there is a potential problem: Fish that have offspring earlier tend to produce ones that are less viable.

Those fish could continue to produce fewer and fewer fertile offspring until the fishery industry is in danger of collapsing.

"It can be a downward spiral," said Joseph G. Kunkel, a professor at the University of Massachusetts at Amherst studying marine life. "If it's physiological, we'll have the same old codfish one day. But if it isn't ... it has tremendous consequences for codfish and haddock."

Many fishermen scoff at the suggestion that fish are becoming smaller because of overfishing.

"It's only because they don't have a lot of food now," said Anton Stetzko, of Orleans, who briefly held the world's record for catching the biggest striped bass off Nauset in 1981. That fish was 73 pounds and he regularly caught 40 and 50 pounders back then. Now, he figures the average catch is somewhere between eight and 18 pounds.

Striped bass are coming back and he says their lighter weight is probably because there are so many of them that they are having a tough time finding enough food.

"I think the big fish will be back," he said. "But we have to allow them to grow big."

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