They’ll never win a beauty contest, but flounder have nonetheless been a favorite among seafood diners in Louisiana. They are, however, in trouble — and the problem may be far more complicated than reducing the amount caught, stuffed and baked.
A decline in southern flounder numbers, likely due to a variety of factors, has prompted the state to implement a seasonal closure to allow the flat-shaped “doormats of the sea" to spawn. But efforts to restore the population may run up against a force much bigger than fishing: climate change.
Research is showing that warmer waters cause more flounder to become male, which could mean further trouble for the species. The Gulf of Mexico, along with the world’s oceans, have warmed considerably over recent decades, and that trend is expected to continue as climate change gains pace.
It raises the potential for the proportion of males to eventually far outweigh females, and while further research still needs to be done, marine biologists are concerned.
“If you're following the climate projections that are out there, the prediction is that there will continue to be warming temperatures, which could increase the impact on this species and others,” said Kenneth Erickson, a former graduate research assistant at LSU and lead author of a study published in 2021 that documented a decline in southern flounder numbers across its range.
‘Really didn’t catch them’
Stuffed flounder has long been a staple on Louisiana restaurant menus, and while anglers often don’t set out specifically in search of the fish, their flat, camouflaged bodies are a welcomed sight at the end of the hook.
In areas with beaches — like Grand Isle and the Mississippi Gulf Coast — flounder “gigging” is common, where anglers wade into the water to catch them by hand with a spear-like gig.
Flounder move offshore to spawn in the fall, and fishers have grown accustomed to catching them during their “runs.” Commercial shrimpers also net them alongside their crustacean targets, giving them a supplementary source of income.
But the decline has become apparent, not only on the Gulf Coast but along the Atlantic as well. The Louisiana Department of Wildlife and Fisheries presented an assessment a few years back that showed spawning-age females at a record low in 2018.
The Wildlife and Fisheries Commission responded by implementing a closed season that began in 2022. That means keeping flounder is banned from Oct. 15 through Nov. 30, including for shrimpers, who must throw them back when hauled up in their nets during that time. A recreational fishing limit of 10 per person, per day also remains in effect during the rest of the year.
Warmer waters can lead to more male flounder being produced. Scientists are concerned over the long-term effects. Jeff Bruhl holds a flounder in Lake Pontchartrain in 2014.
Chris Schieble, the department’s director of marine fisheries, said it appears the closure may be helping in the numbers seen so far, but there may also be other factors at work. Low rivers and drought have resulted in saltier water in estuaries the past couple years, which has led to better catch numbers for a variety of species.
Other Gulf Coast states have either a closed season or a limit on the size and number of flounder that can be caught, said Schieble.
Brandon Ballay, who has been a fishing guide out of Venice for more than three decades, said the past couple years have been great for flounder, but the previous few were terrible. Much depends on the river levels in the Venice area, he notes.
“There was about a two-, three-year window where we really didn't catch them. You’d catch one here, one there,” said Ballay, 50. “Last year and this year — I mean, going out and catching a limit of them on a fairly regular basis.”
‘One more thing’
While the state’s bid to boost the flounder population may certainly help, its biologists are also well aware of the threat of warming waters.
Advocate staff photo by Ian McNulty - Whole stuffed flounder has been a menu mainstay at Middendorf's Restaurant for generations.
Schieble said part of the department’s research involved touring flounder hatcheries that experimented with the effect of warmer water on flounder. Another of the department’s biologists was also one of the co-authors of the study that Erickson led.
The issue has to do with how flounder develop into males or females. It does not happen before they hatch — or not exactly — and stressors such as warmer waters at the start of their lives can cause more to become male, according to scientists at North Carolina State who published a study on the subject in 2019.
Because of those stressors, some flounder end up with female genetics but male sex organs, said Jamie Mankiewicz, the lead author.
An optimal temperature to produce an equal ratio of males and females was around 23 degrees Celsius (73.4 Fahrenheit) for North Carolina, the researchers note. The problem intensifies as the water warms, with an increasing percentage of the fish becoming male. A separate study in Texas cited by Schieble found around 18 degrees Celsius (64.4 Fahrenheit) to be the optimal level.
Similar effects have been seen in Japanese flounder as well as other species, such as sea turtles, researchers say. Heat is not the only stressor that can cause such a change among flounder, the researchers note.
While it may seem logical that narrowing the window for producing female flounder has and will contribute to a decrease in the overall population, that question was outside the scope of the North Carolina study — and one that would require lots more scientific research to pin down, said John Godwin, another of the study’s authors.
There are, however, obvious reasons to worry over the long-term effects of potentially adding another challenge to the struggling southern flounder population — “one more thing they have to deal with,” as Mankiewicz put it.
“I think you can safely say that southern flounder in the Gulf and along the southeast Atlantic coast are in trouble,” said Russell Borski, another of Mankiewicz’s co-authors. “The populations have declined. And again, the cause of that is uncertain. There are probably several contributing factors, like overfishing maybe, maybe habitat — who knows, maybe the temperature.”