Climate change could further damage troubled flounder populations | Environment

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Although it will never win a beauty contest, flounder is still a favorite among seafood diners in Louisiana. But they are in trouble. And the problem can be much more complex than reducing the amount that is caught, packed and burned.

Declining numbers of southern flounder, likely due to a variety of factors, have led the state to implement seasonal closures to allow flat-shaped “marine doormats” to spawn. But efforts to restore the population may face difficulties. There is a much bigger impact than fishing: climate change.

Research has shown that warmer ocean temperatures lead to more male flounders, which could mean further problems for the species. The Gulf of Mexico, like the world’s oceans, has warmed significantly in recent decades, and that trend is expected to continue as climate change accelerates.

More research is needed, but marine biologists are concerned that males may eventually far outnumber females.

“If we’re following the climate projections that are out there, we predict that temperatures will continue to rise, potentially increasing impacts on this species and other species,” said Kenneth Erickson, a former graduate research assistant at LSU. he says. He was the lead author of a study published in 2021 that documented declining numbers of southern flounder across their range.

“I really couldn’t catch it.”

Stuffed flounder has long been a staple on Louisiana restaurant menus, and although anglers don’t specifically go out looking for the fish, their flat, camouflaged bodies on the tip of a hook are a welcome sight.

Flounder “gigging” is common in areas with beaches such as Grand Isle and the Mississippi Gulf Coast, where anglers wade through the water and catch the flounder by hand with a spear-like gig.

Flounder migrate offshore to spawn in the fall, and fishermen are accustomed to catching them during their “runs.” Commercial shrimp fishing also captures shellfish as a supplementary source of income.

However, declines are evident not only along the Gulf Coast but also along the Atlantic Ocean. Several years ago, the Louisiana Department of Wildlife and Fisheries released an assessment showing that the number of breeding-age females in 2018 was the lowest on record.

The Wildlife and Fisheries Commission responded by implementing a closed fishing season starting in 2022. This means that raising flounder will be prohibited from October 15th to November 30th. This includes shrimping, during which the flounder must be thrown back into the net. The recreational fishing limit remains at 10 fish per person per day for the remainder of the year.







Mmm, delicious!Speckled trout, redfish, flounder, black drum and more on Lake Pontchartrain Causeway

Warmer water temperatures may produce more male flounder. Scientists are concerned about the long-term effects. Jeff Brühl holds a flounder on Lake Pontchartrain in 2014.




Chris Schieble, the department’s director of marine fisheries, said the closures appear to be contributing to the numbers seen so far, but other factors may also be at play. Over the past few years, river depletion and drought have increased the salinity of estuary waters, resulting in increased catches of various species.

Schieble said other states on the Gulf Coast have closed fishing periods or have limits on the size and number of flounder that can be caught.

Brandon Valley, who has been a fishing guide in Venice for more than 30 years, said the past few years have been great for flounder, but the past few have been terrible. Much depends on the water levels of the rivers in the Venice area, he points out.

“There was a period of about two or three years where we didn’t actually catch them. “We caught one here and one there,” said Barei, 50. “Last year and this year, I mean, we went out pretty regularly and caught a consistent number.”

‘one more’

While the state’s efforts to boost the flounder population may certainly help, state biologists are also well aware of the threat of warming water temperatures.







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Advocate Staff Photo: Ian McNulty – Whole stuffed flounder has been a mainstay at Middendorf’s restaurants for generations.


Schieble said part of the department’s research included touring a flounder hatchery and experimenting with the effects of warm water on flounder. Another biologist in the department was also a co-author on the study led by Erickson.

This issue has to do with how the flounder develops into a male or female. Scientists at North Carolina State University, who published a study on the topic in 2019, say it doesn’t happen before hatching, but rather when water temperatures rise early in their life. Stress factors may increase the number of individuals who become male.

Lead author Jamie Mankiewicz said these stressors cause some flounders to develop male reproductive organs even though they are genetically female.

The researchers noted that in North Carolina, the optimal temperature for maintaining an equal ratio of males to females was around 23 degrees Celsius (73.4 degrees Fahrenheit). The problem worsens as water temperatures rise, and the proportion of fish that become male increases. Another study in Texas cited by Schieble found that the optimal level is about 18 degrees Celsius (64.4 degrees Fahrenheit).

Researchers say similar effects have been seen not only in flounder but also in other species such as sea turtles. Researchers note that heat is not the only stress factor that can cause such changes in flounder.

While it may seem logical that narrowing the production window for female flounder has and will continue to contribute to overall population declines, that issue is outside the scope of the North Carolina study; More scientific research will be needed to find out. said John Godwin, one of the study’s authors.

But there are clear reasons to be concerned about the long-term effects of potentially adding new challenges to struggling southern flounder populations. In Mankiewicz’s words, “It’s one more thing they have to deal with.”

“I think it’s safe to say that southern flounder in the Gulf and along the southeastern Atlantic coast are in trouble,” said Russell Borski, one of Mankiewicz’s co-authors. “Populations have declined. And again, we don’t know why. There are probably several factors, including overfishing, habitat, and temperature.”

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