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Southern Flounder
Sample fish from a pond that was harvested; the southern flounder were then stocked.
flounder: to struggle clumsily or helplessly.
southern flounder: a species of laterally compressed fish ranging along the Gulf of Mexico from northern Florida southward into Mexico and along the Atlantic coast from North Carolina to northern Florida.(1)
Do you wonder what the relation is? So do I. The southern flounder, Paralichtys lethostigma, is the largest of more than twenty-five species of flatfishes found in Texas coastal waters. It is commercially and recreationally sought after and accounts for more than ninety-five percent of the state's flounder harvest. During the migration from October to December, hundreds of lanterns can often be seen lighting the way for fisherman in search of this favorite catch.(2)
Flounder, as well as many other flat fish, have an established market worldwide, and there is considerable interest in southern flounder culture because of the high market value and ability to grow in fresh or brackish water. The commercial catch of flounder in the U.S. has declined from 20,000 metric tons (MT) in the mid 1980s to a "mandated quota" of about 5,000 MT in 1998.(1) The decline isn't due to a loss in popularity. The numbers, at least of southern flounder, are decreasing.
Though we know quite a lot about southern flounder, compared to some other fish on conservation watch, such as spotted seatrout, we know relatively little. Here is some of the stuff we do know, though.
Spawning
Mature southern flounder begin migrating out of rivers, estuaries, and bays between mid October and mid November to spawn in the warmer offshore water of the Gulf stream. Some elect to stay behind, but most will move out into the Gulf for the winter. Once offshore, spawning takes place between November and February. Females spawn every three to seven days, releasing between 44,000 and 63,000 eggs per spawn. Although this per-spawn number is comparatively low to other species of fish with the same weight, total egg production is similar if all the egg batches are tallied up. Each egg is about one millimeter in diameter, nearly transparent with a single oil droplet, and very buoyant.(1) Adults return to their original bays and estuaries soon after spawning. However, the yearly migration does reshuffle the deck to some extent; some flounder elope to territories different from where they originated.(3) The spring homecoming is gradual, unlike the large concentrations characteristic of the fall emigration.(2)
Growth
Larval flounder feed on zooplankton in offshore waters for thirty to sixty days before they are washed through inlets into bays and estuaries and seek shallow grassy areas near Gulf passes. At this time, they look like other fish, with eyes on either side of the head and swimming with a side-to-side motion. During metamorphosis, which begins after that 30-60 day post-hatch interval, the right eye slowly migrates to the left side of the head, the jaw twists slightly, the left side darkens to brown while the right lightens to white, and the fish changes to an up-and-down swimming motion. Metamorphosis is complete in about two to three weeks, when a body length of about one-half inch is reached.(1)
As with other flat fish, the flounder's sex is not determined until after metamorphosis. Once that's resolved, it's as if male and female southern flounder are two different species. Females grow approximately three times faster than males, though both are sexually mature at two years of age.(1) Males usually don't live longer than three years, or reach a length over fourteen inches. Females live about six years and often reach twenty-five inches, by comparison.(2)
Juvenile flounder feed mainly on crustaceans, but include more fish in their diet than anything else as they grow (though brown shrimp are a favorite of both juvies and adults in Galveston Bay). Unlike most predatory fish which eat larger fish as they grow larger themselves, flounder just eat higher numbers of the same ol' small fish.(3)
In addition to their elders' ambushing tactics, young flounder will also feed aggressively at the surface. Maybe this is the safer method when you're small in size since the extended family (i.e. other southern flounder) are sometimes cannibalistic.(1) As young flounder are no doubt told when they hatch, "you'll see things my way once your eyes come together."
Flounder will eat four to eight percent of their body weight every twenty-four hours. Feeding activity is highest during water temperatures of 61-77F and during the three-day periods following a first quarter moon and before a new moon.(3) Metamorphosed flounder feed by partly burying themselves in the sand and ambushing prey in a rapid upward lunge. This, accompanied by a vacuuming mouth, leads to a swift demise for the unlucky passerby. Flounder have excellent camouflage because, like many other fish, they can change color and skin pattern to mimic the surrounding environment. Pigment-containing cells in the flounder's skin react to light levels around the body and adjust accordingly; blending in with whatever rocks, shells, sand, mud, etc. is around it.(1) A small body cavity and the absence of an air bladder help the flounder sit on bottom, and large optic lobes in the brain aid in vision. Southern flounders' ability to bury themselves is also an evolutionary specialty. A flounder can bend its dorsal and anal fins, which creates a depression. All of these adaptations allow the flounder to occupy its specialized niche in the ecosystem. Southern flounder in particular are considered a near-top predator in the food web; they possess bigger mouths and larger curved teeth than other species of flounder.(4)
Management
As shown by Texas Parks & Wildlife Department's fishery-independent monitoring program, southern flounder populations have been steadily declining statewide over the last twenty-five years. The Gulf States Marine Fisheries Commission has also expressed concern regarding this decline. The main causes for the depleted populations are thought to be overfishing, bycatch, temperature increases, and nursery habitat destruction.(5)
Spotted seatrout and red drum sale was banned in 1981. Comparatively, flounder regulations weren't instituted until 1988, but flounder fishing mortality has still increased steadily since 1989. Much of the fishing pressure comes during the emigration to offshore waters before many flounder are able to spawn for the first time. The buyback program for commercial shrimping license holders, instituted in 1999, has retired fifty-seven percent of bay/bait licenses and decreased the overall yearly bycatch significantly. Even so, bycatch historically condemns up to 9.7 million individuals per year. Higher winter temperatures hinder egg hatching and increase predation on larvae and early juveniles, besides having an effect on sex determination.(6)
Regulations up to this point have favored southern flounder populations but haven't reversed the overall decline:
1988: Trammel and gill nets banned. Recreational bag limit 20/day (40 in possession); minimum length 12 inches.
1990: Fifty percent composition rule for shrimp nets (shrimpers can only keep non-shrimp catch up to fifty percent of the weight of the shrimp caught).
1996: Bag limits: 10/day recreational, 20/possession (formerly 20/day and 40/possession), 60/day commercial (formerly 100/day). Minimum length increased to 14 inches. Recreational bag limit applied to shrimping vessels.
1999: Limited entry/buyback program implemented for commercial finfish license holders.
2000: Bycatch Reduction Device requirement implemented (a device to reduce finfish capture in shrimp nets). Elimination of commercial fishing in nursery areas.
2006: Recreational possession limit reduced to 10 fish (same as daily bag limit).
2009: Recreational limit reduced to 5/day, 5 in possession, except November 2/day (2 possession) rod and reel only, no gigging. Commercial bag limit reduced to 30/day, except month of November closed to all commercial harvest.(6)
Hatchery Programs
Here is where conservationists are trying to tip the scales back into the flounders' favor. Three facilities, the CCA/AEP Marine Development Center in Corpus Christi, Perry R. Bass Marine Fisheries Research Station in Palacios, and Sea Center Texas in Lake Jackson, in conjunction with the University of Texas Marine Science Institute (UTMSI), began development of a stock enhancement program for southern flounder in 2004. These research centers, together, have already developed successful stock enhancement programs for red drum and spotted seatrout, and while the southern flounder program is still in its infancy, it's made significant progress since its beginning.(7)
The requirements for successfully spawning and raising flounder are almost completely opposite those of red drum and seatrout. They spawn for only a short season in winter, require three males for every female, and hatchlings grow twice as slow. This is a tough species to work with. Plus, Sea Center and the other facilities are hampered by the fact that everything is set up for red drum and seatrout, so along with developing completely different techniques for flounder stock enhancement, they also have to create completely different infrastructure and acquire completely different resources.(7)
In the first year, UTMSI provided Sea Center with 2.4 million eggs. Twelve fish were the result, and the brood stock produced only a single round of (unfertilized) spawning. It's come a long way since then. Since 2004, the program has stocked 20,000 fish between Aransas, Galveston, and Sabine Lake. Sea Center has about 600 brood stock on site, and this year marked the first naturally fertilized spawning, a BIG step. In conjunction with successfully developed strip spawning techniques, the team hopes to expand to three successful spawns per year.(7)
For concerned flounder lovers, the best way to help this species rebound is to obey the limits set out by Texas Parks & Wildlife, especially during the shut down time (November) as it is a very critical time for spawning.(7) The current bag limits for flounder are 5/2: daily bag is five fish except for the period of November 1-30 when the daily bag is two fish and flounder may be taken only by pole and line; possession limit is equal to the daily bag. Gigging limits are the most important limits on flounder harvest. They are currently 5 fish/day for recreational and 30 fish/day for commercial fishers during all months except November when no gigging and no commercial sale is allowed. Current limits can always be found on the Texas Parks & Wildlife website.
Southern flounder, and flounder in general, are an interesting, appetizing, and important recreational and commercial fish that we don't know nearly enough about. We know they're disappearing, and that's enough to do something, right? Hopefully, conscientious anglers will feel the same need for action to conserve the southern flounder as they have for the spotted seatrout and redfish. Undoubtedly, those who have already worked for flounder conservation could sure use a few more lifelines.
Footnotes
(1) H.V. Daniels, "Species Profiles: Southern Flounder" (Southern Regional Aquaculture Center: 2000) 1-4.
(2) "Southern Flounder (Paralichthys lethostigma)," Texas Parks & Wildlife, 26 June 2011 <http://www.tpwd.state.tx.us/huntwild/wild/species/flounder/>.
(3) "Biological Info: Southern Flounder," Lousiana Fisheries, 26 June 2011 <http://www.seagrantfish.lsu.edu/biological/misc/southernflounder.htm>.
(4) "Week 3 - Southern Flounder," Dans Island Ecology, 26 June 2011, <https://sites.google.com/site/dansislandecology/summary-3/week-3-2>.
(5) Suraida Nanez-James, Gregory Stunz, Scott Holt, "Habitat Use Patterns of Newly Settled Southern Flounder, Paralichthys lethostigma, in Aransas-Copano Bay, Texas" (Coastal and Estuarine Research Federation: 2008) 1-10.
(6) "Status of the Southern Flounder Population in Texas" (presentation by Texas Parks & Wildlife Department, Coastal Fisheries Division, during a flounder workgroup) <www.ccatexas.org/files/2009/03/tpwdflounderwgpresentationfinal.pdf>.
(7) David Abrego, Facility Director of Sea Center Texas, Phone interview, 6 July 2011.
southern flounder: a species of laterally compressed fish ranging along the Gulf of Mexico from northern Florida southward into Mexico and along the Atlantic coast from North Carolina to northern Florida.(1)
Do you wonder what the relation is? So do I. The southern flounder, Paralichtys lethostigma, is the largest of more than twenty-five species of flatfishes found in Texas coastal waters. It is commercially and recreationally sought after and accounts for more than ninety-five percent of the state's flounder harvest. During the migration from October to December, hundreds of lanterns can often be seen lighting the way for fisherman in search of this favorite catch.(2)
Flounder, as well as many other flat fish, have an established market worldwide, and there is considerable interest in southern flounder culture because of the high market value and ability to grow in fresh or brackish water. The commercial catch of flounder in the U.S. has declined from 20,000 metric tons (MT) in the mid 1980s to a "mandated quota" of about 5,000 MT in 1998.(1) The decline isn't due to a loss in popularity. The numbers, at least of southern flounder, are decreasing.
Though we know quite a lot about southern flounder, compared to some other fish on conservation watch, such as spotted seatrout, we know relatively little. Here is some of the stuff we do know, though.
Spawning
Mature southern flounder begin migrating out of rivers, estuaries, and bays between mid October and mid November to spawn in the warmer offshore water of the Gulf stream. Some elect to stay behind, but most will move out into the Gulf for the winter. Once offshore, spawning takes place between November and February. Females spawn every three to seven days, releasing between 44,000 and 63,000 eggs per spawn. Although this per-spawn number is comparatively low to other species of fish with the same weight, total egg production is similar if all the egg batches are tallied up. Each egg is about one millimeter in diameter, nearly transparent with a single oil droplet, and very buoyant.(1) Adults return to their original bays and estuaries soon after spawning. However, the yearly migration does reshuffle the deck to some extent; some flounder elope to territories different from where they originated.(3) The spring homecoming is gradual, unlike the large concentrations characteristic of the fall emigration.(2)
Growth
Larval flounder feed on zooplankton in offshore waters for thirty to sixty days before they are washed through inlets into bays and estuaries and seek shallow grassy areas near Gulf passes. At this time, they look like other fish, with eyes on either side of the head and swimming with a side-to-side motion. During metamorphosis, which begins after that 30-60 day post-hatch interval, the right eye slowly migrates to the left side of the head, the jaw twists slightly, the left side darkens to brown while the right lightens to white, and the fish changes to an up-and-down swimming motion. Metamorphosis is complete in about two to three weeks, when a body length of about one-half inch is reached.(1)
As with other flat fish, the flounder's sex is not determined until after metamorphosis. Once that's resolved, it's as if male and female southern flounder are two different species. Females grow approximately three times faster than males, though both are sexually mature at two years of age.(1) Males usually don't live longer than three years, or reach a length over fourteen inches. Females live about six years and often reach twenty-five inches, by comparison.(2)
Juvenile flounder feed mainly on crustaceans, but include more fish in their diet than anything else as they grow (though brown shrimp are a favorite of both juvies and adults in Galveston Bay). Unlike most predatory fish which eat larger fish as they grow larger themselves, flounder just eat higher numbers of the same ol' small fish.(3)
In addition to their elders' ambushing tactics, young flounder will also feed aggressively at the surface. Maybe this is the safer method when you're small in size since the extended family (i.e. other southern flounder) are sometimes cannibalistic.(1) As young flounder are no doubt told when they hatch, "you'll see things my way once your eyes come together."
Flounder will eat four to eight percent of their body weight every twenty-four hours. Feeding activity is highest during water temperatures of 61-77F and during the three-day periods following a first quarter moon and before a new moon.(3) Metamorphosed flounder feed by partly burying themselves in the sand and ambushing prey in a rapid upward lunge. This, accompanied by a vacuuming mouth, leads to a swift demise for the unlucky passerby. Flounder have excellent camouflage because, like many other fish, they can change color and skin pattern to mimic the surrounding environment. Pigment-containing cells in the flounder's skin react to light levels around the body and adjust accordingly; blending in with whatever rocks, shells, sand, mud, etc. is around it.(1) A small body cavity and the absence of an air bladder help the flounder sit on bottom, and large optic lobes in the brain aid in vision. Southern flounders' ability to bury themselves is also an evolutionary specialty. A flounder can bend its dorsal and anal fins, which creates a depression. All of these adaptations allow the flounder to occupy its specialized niche in the ecosystem. Southern flounder in particular are considered a near-top predator in the food web; they possess bigger mouths and larger curved teeth than other species of flounder.(4)
Management
As shown by Texas Parks & Wildlife Department's fishery-independent monitoring program, southern flounder populations have been steadily declining statewide over the last twenty-five years. The Gulf States Marine Fisheries Commission has also expressed concern regarding this decline. The main causes for the depleted populations are thought to be overfishing, bycatch, temperature increases, and nursery habitat destruction.(5)
Spotted seatrout and red drum sale was banned in 1981. Comparatively, flounder regulations weren't instituted until 1988, but flounder fishing mortality has still increased steadily since 1989. Much of the fishing pressure comes during the emigration to offshore waters before many flounder are able to spawn for the first time. The buyback program for commercial shrimping license holders, instituted in 1999, has retired fifty-seven percent of bay/bait licenses and decreased the overall yearly bycatch significantly. Even so, bycatch historically condemns up to 9.7 million individuals per year. Higher winter temperatures hinder egg hatching and increase predation on larvae and early juveniles, besides having an effect on sex determination.(6)
Regulations up to this point have favored southern flounder populations but haven't reversed the overall decline:
1988: Trammel and gill nets banned. Recreational bag limit 20/day (40 in possession); minimum length 12 inches.
1990: Fifty percent composition rule for shrimp nets (shrimpers can only keep non-shrimp catch up to fifty percent of the weight of the shrimp caught).
1996: Bag limits: 10/day recreational, 20/possession (formerly 20/day and 40/possession), 60/day commercial (formerly 100/day). Minimum length increased to 14 inches. Recreational bag limit applied to shrimping vessels.
1999: Limited entry/buyback program implemented for commercial finfish license holders.
2000: Bycatch Reduction Device requirement implemented (a device to reduce finfish capture in shrimp nets). Elimination of commercial fishing in nursery areas.
2006: Recreational possession limit reduced to 10 fish (same as daily bag limit).
2009: Recreational limit reduced to 5/day, 5 in possession, except November 2/day (2 possession) rod and reel only, no gigging. Commercial bag limit reduced to 30/day, except month of November closed to all commercial harvest.(6)
Hatchery Programs
Here is where conservationists are trying to tip the scales back into the flounders' favor. Three facilities, the CCA/AEP Marine Development Center in Corpus Christi, Perry R. Bass Marine Fisheries Research Station in Palacios, and Sea Center Texas in Lake Jackson, in conjunction with the University of Texas Marine Science Institute (UTMSI), began development of a stock enhancement program for southern flounder in 2004. These research centers, together, have already developed successful stock enhancement programs for red drum and spotted seatrout, and while the southern flounder program is still in its infancy, it's made significant progress since its beginning.(7)
The requirements for successfully spawning and raising flounder are almost completely opposite those of red drum and seatrout. They spawn for only a short season in winter, require three males for every female, and hatchlings grow twice as slow. This is a tough species to work with. Plus, Sea Center and the other facilities are hampered by the fact that everything is set up for red drum and seatrout, so along with developing completely different techniques for flounder stock enhancement, they also have to create completely different infrastructure and acquire completely different resources.(7)
In the first year, UTMSI provided Sea Center with 2.4 million eggs. Twelve fish were the result, and the brood stock produced only a single round of (unfertilized) spawning. It's come a long way since then. Since 2004, the program has stocked 20,000 fish between Aransas, Galveston, and Sabine Lake. Sea Center has about 600 brood stock on site, and this year marked the first naturally fertilized spawning, a BIG step. In conjunction with successfully developed strip spawning techniques, the team hopes to expand to three successful spawns per year.(7)
For concerned flounder lovers, the best way to help this species rebound is to obey the limits set out by Texas Parks & Wildlife, especially during the shut down time (November) as it is a very critical time for spawning.(7) The current bag limits for flounder are 5/2: daily bag is five fish except for the period of November 1-30 when the daily bag is two fish and flounder may be taken only by pole and line; possession limit is equal to the daily bag. Gigging limits are the most important limits on flounder harvest. They are currently 5 fish/day for recreational and 30 fish/day for commercial fishers during all months except November when no gigging and no commercial sale is allowed. Current limits can always be found on the Texas Parks & Wildlife website.
Southern flounder, and flounder in general, are an interesting, appetizing, and important recreational and commercial fish that we don't know nearly enough about. We know they're disappearing, and that's enough to do something, right? Hopefully, conscientious anglers will feel the same need for action to conserve the southern flounder as they have for the spotted seatrout and redfish. Undoubtedly, those who have already worked for flounder conservation could sure use a few more lifelines.
Footnotes
(1) H.V. Daniels, "Species Profiles: Southern Flounder" (Southern Regional Aquaculture Center: 2000) 1-4.
(2) "Southern Flounder (Paralichthys lethostigma)," Texas Parks & Wildlife, 26 June 2011 <http://www.tpwd.state.tx.us/huntwild/wild/species/flounder/>.
(3) "Biological Info: Southern Flounder," Lousiana Fisheries, 26 June 2011 <http://www.seagrantfish.lsu.edu/biological/misc/southernflounder.htm>.
(4) "Week 3 - Southern Flounder," Dans Island Ecology, 26 June 2011, <https://sites.google.com/site/dansislandecology/summary-3/week-3-2>.
(5) Suraida Nanez-James, Gregory Stunz, Scott Holt, "Habitat Use Patterns of Newly Settled Southern Flounder, Paralichthys lethostigma, in Aransas-Copano Bay, Texas" (Coastal and Estuarine Research Federation: 2008) 1-10.
(6) "Status of the Southern Flounder Population in Texas" (presentation by Texas Parks & Wildlife Department, Coastal Fisheries Division, during a flounder workgroup) <www.ccatexas.org/files/2009/03/tpwdflounderwgpresentationfinal.pdf>.
(7) David Abrego, Facility Director of Sea Center Texas, Phone interview, 6 July 2011.