A fish-eye view of management through an evolutionary lens

STONY BROOK, NY. Fishing, whether for business or pleasure, is regulated by agencies that impose size and catch limits on commonly exploited species. But the practice of selectively harvesting only the largest fish may be causing the average size of fish to decrease. So say David O. Conover, professor at the Marine Sciences Research Center at Stony Brook University, and graduate student Stephan B. Munch whose paper "Sustaining Fisheries Yield over Evolutionary Time Scales" appears in the July 5 issue of Science.

In their New York Sea Grant-funded research, Conover and Munch, posit that fishery management plans ignore the potential for evolutionary change in harvestable populations such as commercially important fish species. They have been able to observe such evolutionary trends in experimental fish populations.

Using the Atlantic silverside (Menidia menidia), a small common marine fish, Conover found that in populations where large individuals were selectively removed, the average size of the silversides declined dramatically in just four generations. Conversely, when the smaller individuals were selected out, the average size increased.

The authors believe that fish harvesting has impacts that go beyond the immediate ecological response to changes in fish abundance. "Our study illustrates how well-intentioned management plans that appear to maximize yield on ecological time scales may have the opposite effect after accounting for evolutionary dynamics," reports Conover. Fishing may have evolutionary impacts that lead to genetic changes in the population that affect the growth rates of fish and ultimately the productivity of harvested populations.

Managing fisheries is a challenging balancing act between sustaining fish stocks worldwide and the importance of fishing to the global economy.

"In New York State alone," says Jack Mattice, Director of New York Sea Grant, "the commercial fishing, recreational fishing, and the seafood industries make a $11.5 billion contribution to the state's economy and employ over 100,000 people." The lifeblood of these industries is healthy fisheries.

"More work is needed to determine whether or not evolutionary changes are occurring in wild populations" said Conover. But if so, the authors make two suggestions about how to manage fisheries for sustainable harvest over the long haul: 1. a rethinking of reliance of minimum size restriction as a basic management tool and 2. the establishment of no-take reserves or marine protected areas that may, if properly designed, provide for the maintenance of natural genetic variation of marine life.

Contact:
David Conover, New York Sea Grant Researcher, Professor of Marine Science, Stony Brook University, (O) 631-632-8667
Jack Mattice, Director, New York Sea Grant, Stony Brook University, (O) 631-632-6905

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