Study: Fishing changes population
Monday, July 16, 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." 

Copyright 2001, Associated Press
All Rights Reserved
    
    

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