S​melt Population Declining

By Anjanette Riley - Published May 18, 2015

smeltThis smelt, at 6 inches, is about an inch longer than typical for the prey fish. A 2014 study provided new data on the dwindling smelt population.(Photo by James Roberts and Tomas Höök)

The reasons for the dwindling smelt population in the Great Lakes to near historic lows are more complicated than previously believed, new research suggests.

Although results of the 2014 study show that the number of smelt surviving their first few months actually has been rising since 2000, the increase in hatchlings isn't producing more adults. Whatever the cause, the loss of adult rainbow smelt is keeping the population on a downward trend even as offspring survival improves.

Researchers from the U.S. Geological SurveyIllinois-Indiana Sea Grant and the U.S. Environmental Protection Agency's Great Lakes National Program Office discovered the unexpected increase in offspring after analyzing about 40 years of fisheries data using a novel modeling technique. 

The researchers speculate that the drop in the number of adult smelt may be allowing hatchlings to thrive. Adult rainbow smelt frequently eat their offspring. Fewer adults means fewer predators for juvenile smelt.

The need to find food in a lake infested with millions of quagga and zebra mussels that filter out plankton may be driving adults further out into the lake and away from spawning grounds, the researchers said.

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Causes of Great Lakes smelt population decline are complex