Winter Flounder Can Be Traced Using Their Inner Ear Bones, Say Researchers

In an effort to restore the declining populations of winter flounder along the East Coast of the U.S., researchers from the University of New Hampshire turn to the fishes' inner ear bone. Known as the otoliths, these bones provide vital information regarding the fish's age and chemical elements found in its environment. All of this helps researchers understand the estuaries these juveniles grow up in, according to the University of New Hampshire.

This research was conducted by David Bailey, a UNH graduate student, Elizabeth Fairchild, UNH research assistant professor of biology, and Linda Kalnejais, assistant professor of oceanography. Together they found that juvenile winter flounder share similar chemical signatures on their otoliths if they are in estuaries within roughly 7.5 miles of each other. According to their study, these chemical signatures are influenced by the unique geology and water chemistry of the watersheds that empty into the estuaries they inhabit.

"We don't know where the adults actually come from, which specific bay," Fairchild said in a statement. "We wanted to know if we could say, yes, that's a Great Bay fish, or that's a Narragansett Bay fish, or a Boston Harbor fish. If we can figure that out, we can determine which estuaries in the Northeast are the most essential in terms of providing valuable habitat for winter flounder and protect those places."

The researchers ran samples of the winter flounder's otoliths collected from 12 locations in estuaries and shallow coastal waters ranging from the Navesink River in New Jersey, and northward to New Hampshire's Great Bay. The inner ear bones were then examined through a mass spectrometer to determine the correlation between chemical make-up and location.

The results of their study using otolith chemistry, recently published in the journal Transactions of the American Fisheries Society, prove to have a 73 percent accuracy rate when tracing juvenile winter flounder back to their brackish homes. This provides a new tool for monitoring the species.

Winter flounder are valued for their taste. Known on many menus as simply flounder, in 2013 the fish were valued at roughly $10 million. Fairchild explained that despite strict fishing regulations, this species has been facing a population decline over the past two decades along the East Coast. Juvenile winter flounder must eventially swim out to deeper offshore waters in order to survive but the estuaries in which they develop are being negatively impacted by warming waters and land development pressures. 

"This research is important in terms of environmental protection, trying to figure out which estuaries are producing the most number of fish for the population where people can actually fish for them, and trying to protect those estuaries so we don't harm the winter flounder," Bailey added. "You wouldn't want to dredge an area if you know that's the prime area that produces fish for a Gulf of Maine winter flounder fishery."

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