Much mystery remains on annual flounder migrations
A powerful spring tide turned the marshes into a grassy lake during the previous evening, but a southerly breeze began pushing water out toward the Gulf of Mexico.
“Let it drift with the tide,” the grandfather instructed.
The young angler tossed a live shrimp under a popping cork far up into a ditch draining the marshes. As the cork began to drift down with the current, she popped it. The cork never returned to the surface.
“Set the hook!” the grandfather shouted enthusiastically.
The youngster yanked back, bowing the rod. The enraged creature kicked up a cloud of goo in that little drain. Soon, a large, flat splotchy-brown object materialized on the surface next to the boat.
“Got’em, Grandpa!” she screamed. “It’s a huge flounder. My first one.”
Twice each year, flounder migrate from inland waters to the deep Gulf and back, although some stay in the bays and estuaries all year long. Much of that journey remains a mystery.
“In the fall, flounder head offshore after those first cold fronts hit in about October or November,” said Jason Adriance, a fisheries biologist with the Louisiana Department of Wildlife and Fisheries. “We suspect that the mature fish head offshore to spawn. A lot of the immature fish tend to stay in the estuary over the winter.”
Plenty of questions
Most flounder probably start their long swim back from the depths toward inshore waters in January or February, but weather could determine when flounder head north. Deep waters stay more stable all year long. During a severe winter, such as the most recent one, the depths could remain much warmer than the shallow bays and marsh ponds later into the spring.
“We still don’t have much information on what happens to flounder after they leave the estuaries to go spawn,” Adriance said. “There have been a few studies where they tagged flounder leaving the estuaries heading offshore, but they never got any returns on flounder coming back in during the spring. The presumption has always been that flounder come back later in the spring after going offshore over winter to spawn, but there’s still questions and data gaps in how many flounder actually come back into the estuaries.”
Few people venture into the Gulf in January to fish for flounder in 200 feet of water, hence the lack of tag returns from offshore. Snapper fishermen and others dropping baits to the reefs might catch an occasional flounder in deep water, much to their surprise, but most people think of flounder as a shallow water fish that likes weedy shorelines.
“There’s still much we don’t know about flounder movement and migrations,” Adriance said. “There’s still questions about whether flounder in the spring are returning from offshore, they were in the lower parts of the estuaries or just nearshore.”
Two flounder species
By late March or April, anglers might start finding flounder in the bays and estuaries or around the barrier islands. Look for them around grassy shorelines, reefs, beaches and other places where they can ambush food. Anglers who locate a chokepoint, such as a pass leading to the Gulf, might find flounder stacked up as they make their way toward inland waters. In the right spot, anglers could quickly load a boat with spring flatfish.
Anglers might catch two flounder species, southern and Gulf. Identified by three ocellated black spots that form a triangle, Gulf flounder don’t grow as large as southern flounder. The world record weighed 7 pounds, 2 ounces. Gulf flounder prefer deeper, saltier waters than southern flounder. Look for them around nearshore reefs, but they could go to waters more than 300 feet deep.
More familiar to most anglers, southern flounder show splotchy spots all over their brown sides. Southern flounder can exceed 20 pounds. The Louisiana state record southern flounder weighed 13.06 pounds. Gary Hargis caught that fish in June 1998 near South Pass, one of the river outlets to the Gulf.
“Southern flounder are the species anglers encounter most,” Adriance said. “Gulf flounder tend to be more of an offshore species and they’re not as prevalent as southern flounder.”
Most male southern flounder remain farther offshore or in nearshore waters and seldom grow longer than 14 to 15 inches. Look for them around reefs with cover and flat surfaces in waters about 30 to 60 feet deep. In the fall, male flounder gather in the passes, waiting for females ready to spawn to head offshore.
Female southern flounder
Like in most fish species, southern flounder females normally grow larger and faster than males because they must carry the future generations during spawning season. Typically, by their first year, female southern flounder can grow to about 13 inches long.
By some estimates, female southern flounder probably make up about 75 percent of the inshore flounder population during warmer months. The other 25 percent consist mainly of smaller males and juveniles of indeterminate sex.
“Female flounder tend to grow faster and get bigger than males, so a lot of the harvest is dominated by female fish,” Adriance said. “The males tend to grow a little slower and stay smaller. It’s quite possible that a female will be big enough to keep before a male. Louisiana doesn’t have a size limit on flounder, so it’s up to the people on how big of a fish they want to keep.”
Since more females stay in inshore waters longer than males, plus grow larger and faster, fishing pressure more heavily impacts the female southern flounder population. That reduces their reproductive potential.
In addition, studies show that when larval fish come into the marshes and estuaries, water temperature determines their development. If the water in the estuaries warms too fast in the spring, most of the young flounder become males, which can also reduce the reproduction potential of the entire population.
A population issue
For more than a decade, anglers reported low flounder numbers across the Gulf Coast, including in Louisiana. Things have begun to pick up in the past few years. In 2022, the state changed the flounder regulations to permit more spawners to live longer. Louisiana anglers can keep 10 flounder per day with no size limits. The state prohibits any flounder harvests from Oct. 15 through Nov. 30 each year.
“With flounder, the issue in Louisiana has never been overfishing,” Adriance said. “We don’t have too many anglers taking too many flounder. It’s a population issue. The spawning population is too low. We need to build up that spawning biomass. That’s what led to the regulations we put in place in 2022 to rebuild that spawning population. That closure in the fall allows as many females to get offshore to spawn as possible by having no harvest during that crucial offshore migration period.”
Most flounder probably come to the boat by fishermen seeking redfish or speckled trout. All three species hit many of the same baits and lures, especially shrimp and cocahoe minnows or things that look like natural prey. While few people leave the docks to intentionally target flounder, nobody likes to let one of these delicious fish go.
Where to catch flounder
Despite the low numbers, anglers can still find some good places to catch flatfish in the Sportsman’s Paradise. Any salty to brackish waters from the Pearl River Delta to the Sabine River Delta should hold flounder. Flatfish can tolerate fresh water and regularly appear far upstream in coastal rivers. Ask any bass fisherman who commonly fishes tidal waters.
“The Pearl River Delta is a great area to fish,” said Mike Gallo of Angling Adventures of Louisiana (877-4AAOFLA, www.aaofla.com) in Slidell. “We fish the bayous, jagged shorelines, ponds and marshy sloughs.”
Some better places to catch flounder include any marshy coastal river delta. The marshes between the Rigolets and Chef Menteur Pass in Orleans Parish traditionally hold good flounder populations.
The entire greater Mississippi River Delta region, from Lake Borgne southward, eastward to the Chandeleur Islands and westward around the mouth of the Mississippi River to the Barataria and Terrebonne estuaries also hold flounder. Anglers can also catch flounder around Marsh Island and many other places in the Atchafalaya River Delta and Vermilion Bay.
In Southwestern Louisiana, the marshes between Calcasieu Lake and Sabine Lake and in the lakes themselves offer some of the best flounder action in the state. Between the lakes, Sabine National Wildlife Refuge (www.fws.gov/refuge/sabine) preserves 124,500 acres of marsh.
“Both Sabine and Calcasieu lakes, as well as the marshes between them, are great places to look for flounder and can hold some big ones,” confirmed Tom Adams, Jr. of Fishing Tom Guide Service (318-675-9114, FishingTom.net) in Sulphur. “On the eastern side of Calcasieu Lake, five weirs control the water levels in the marshes. Those marshes hold a lot of flounder.”
We might not know everything about flounder migrations, but we do know what happens to them in Louisiana kitchens. Few fish dishes taste better than flounder stuffed with crabmeat.
