Biological oceanographers Aimee Keller and Grace Klein-MacPhee at the University of Rhode Island’s Graduate School of Oceanography have conducted experiments on winter flounder that suggest that the decline of the species in Narragansett Bay may be the result of elevated winter water temperatures.
In a recent study, reported in the Canadian Journal of Fisheries and Aquatic Sciences, Keller and Klein-MacPhee tested the direct link between warmer temperatures and the growth and survival of winter flounder larvae and examined the relationship between temperature and the components leading to larval fish. The study was conducted in the mesocosms of the Marine Ecosystem Research Laboratory at the URI Narragansett Bay Campus.
Keller and Klein-MacPhee’s study, funded by a U.S. Environmental Protection Agency Cooperative Agreement with the National Academy of Sciences of the National Research Council, found that the cumulative impact of warmer temperatures on the early life history of winter flounder from hatching through the late larval stage resulted in 10-16% fewer larvae surviving to the metamorphosis stage at 6 weeks.
Winter water temperatures in Narragansett Bay have significantly increased over the past 40 years. The warmer temperatures impact the winter-spring bloom, having an influence on the availability of food to higher level organisms. In a previous study by Keller, she found that the winter-spring bloom failed to occur in warm systems, similar to its failure to appear in the Bay in recent years. Elevated temperatures may also lead to increased metabolic activity of potential predators, leading to increased predation rates.
Although overfishing plays a role in the population decline, other factors are important in controlling the spawning and survival of winter flounder. Annual abundance is negatively correlated with winter temperature, indicating that warmer temperatures during spawning result in fewer fish.
“These results, together with the potential for increased predation as a result of elevated winter water temperature, suggest that temperature and its impact on the predation rate may play a major role in regulating winter flounder abundance,” said Klein-MacPhee. “Now that we know that this effect exists, regional managers should attempt to incorporate the potential impact of warm winters in their management plans.”
Keller, formerly of Narragansett, received her B.A., M.S. and Ph.D. from the University of Rhode Island. She now lives in Washington state. Klein-MacPhee, a resident of Narragansett, received her B.A. and M.A. degrees from Boston University, and a Ph.D. from the University of Rhode Island.
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