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Reversal of Undesirable Evolution in Fish

imagePI: Dr. David Conover, Stony Brook University*

*External Grantee

Completed 2009

Decades of intensively harvesting the largest fish, while simultaneously allowing smaller fish to survive and reproduce, has unintentionally resulted in a genetic reprogramming of fish to grow smaller. This unnatural selection has also has created fish that are less fertile and competitively disadvantaged due to their smaller size, posing a major problem for both marine ecosystems and the fishing industry. A 10-year study largely supported by the Institute for Ocean Conservation Science and led by Dr. David O. Conover, Professor and Dean of the Stony Brook University School of Marine and Atmospheric Sciences, has demonstrated for the first time that detrimental evolution in fish can be reversed. Dr. Conover’s study was published in March 2009 in Proceedings of the Royal Society B, and the results provide a strong argument for rethinking key aspects of fishery management policy.

The research was conducted at Flax Pond Marine Laboratory on the north shore of Long Island, NY. Dr. Conover and colleagues captured hundreds of Atlantic silversides (Menidia menidia) from Great South Bay, and divided them into six groups. For five generations, which amounts to approximately five years for the silverside, Dr. Conover and colleagues selectively removed the largest fish from two groups, the smallest fish from two groups, and fish of random size from two groups. After five years’ time, fish in the large-harvested group had a smaller average body size, showing that fishing-induced change occurs rapidly and dramatically. The results of this portion of the study were published in 2002 in the journal Science. In the second phase of the study, researchers allowed five generations of recovery, in which fish were allowed to reproduce naturally with no human interference. Researchers found that body size of the fish gradually rebounded, despite previous theories suggesting that it is impossible to reverse genetic changes. Those results were published in Proceedings B.

Dr. Conover and colleagues estimate that if the largest fish were left unharvested, full recovery of the silverside would take approximately twelve generations in a controlled situation such as the laboratory. Recovery for wild populations of those and other fish could be shorter or longer depending upon the species and environment. For example, it would likely take decades for commercially harvested fish species to return to previously recorded sizes, since they typically have a longer generation time (three to seven years). This time-lag could explain why fish like the cod have not yet rebounded in size or abundance despite the closure of the fishery years ago.

Dr. Conover’s research has provided the first direct experimental evidence that the growth rate of fish, and therefore productivity, can rapidly evolve in response to the pressures of size-selective harvest and can be reversed if allowed to recover without interference. Currently, fishery management plans fail to incorporate these evolutionary dynamics and instead mostly impose minimum size limits, banning the capture of fish below a specific size and promoting capture of the largest fish. Since this unwittingly promotes the evolution of fish to be smaller and less productive, it is essential for fishery management plans to be analyzed and modified to promote sustainable practices and healthy future fisheries. Dr. Conover suggests changing fishery regulations by setting a maximum-size limit would gradually allow fisheries to rebound. Dr. Conover’s research provides significant evidence that many current fishery management plans are unsustainable, and that prompt and widespread change must be implemented in order to restore and maintain the oceans’ fisheries.In addition to Dr. Conover, authors on the Proceedings B paper are Dr. Stephan B. Munch, Assistant Professor in the Stony Brook University School of Marine and Atmospheric Sciences, and Dr. Stephen A. Arnott of the South Carolina Department of Natural Resources Marine Resources Research Institute.

More information

Learn more about Dr. Conover and his research

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