No way back? Species like the cod may be even more vulnerable than biologists assumed.

Not Always More Fish in the Sea

SAN FRANCISCO--New analyses dispute the long-cherished idea that marine fish populations are not particularly vulnerable to extinction and should be able to bounce back quickly after depletion once fishing moratoriums are imposed. The research suggests that overfishing may pose even greater threats to marine life than previously thought.

"All the great sea-fisheries are inexhaustible ... nothing we do seriously affects the number of fish," Darwin's great supporter Thomas Huxley famously said in 1883. Awed by the sheer quantity of eggs a typical marine fish produces, many scientists and fisheries managers today remain convinced that fish are less prone to decline and extinction than other vertebrates. Following recent collapses of fisheries in the North Atlantic, many argued that temporary moratoriums on fishing would allow fish stocks to rapidly bounce back.

But a new analysis of fisheries literature and catch data by evolutionary ecologist Jeffrey Hutchings of Dalhousie University in Halifax, Nova Scotia, contradicts this idea. In work published last year Hutchings showed that for 90 fish stocks, species that suffered more-severe population declines made less-effective recoveries--and that many North Atlantic fish such as cod, haddock, and flatfishes have not yet recovered following recent fishery collapses and subsequent harvest restrictions.

At the Second Symposium on Marine Conservation Biology here on 23 June, Hutchings outlined why we shouldn't expect quick recovery. Using data compiled by his Dalhousie colleague Ransom Myers, Hutchings showed that fishing intensity alone following collapses often has little effect on whether a population recovers; rather, a fish species' particular ecology and life history may largely determine its ability to bounce back. Furthermore, data from many species shows that their high fecundity is balanced by high mortality, so that the population growth rates of marine fish are no greater than those of birds or mammals. Finally, Hutchings demonstrated, fish show no greater variability in population size than birds or mammals, something which had also been believed to make them more resilient to extinction. Hutchings concludes that fish should be considered just as vulnerable to extinction as the birds and mammals whose declines are more conspicuous. "If passenger pigeons swam in the water and cod flew in the air," he said, managers would have been far more aware of the threat.

Conservation biologist Stuart Pimm of Columbia University in New York City says the analysis should put to rest old ideas about the resilience of marine fish. The study "does not just kill a sacred cow," he says, "it kills a sacred herd of cows."

Related sites

Jeffrey Hutchings's home page
Ransom Myers's public database of hundreds of fish stocks