Southern Flounder
William Greenleaf
Introduction
The North Carolina State Saltwater Record for flounder was caught in Carolina Beach by Harold Auten with a flounder weighing a whopping 20 lb. 8 oz. North Carolina State Saltwater Records
Unfortunately, North Carolina does not separate the state record for flounder to indicate the three species of flounder, the Southern Flounder, Gulf Flounder, and Summer Flounder, along the coast. The easiest way to differentiate the three are by the present or absence of spots near the tail; Summer Flounder have five distinct dark spots, Gulf Flounder have three spots, and Southern Flounder have no definitive spots (Burleson, n.d.).
Southern Flounder are dark, brown flatfish that settle along the ocean floor/estuary floor. They go through a metamorphosis between larval stage and juvenile stage that transfixes the right eye onto the left side. They have large mouths and have the ability to camouflage with the muddy and sandy bottom of the ocean and estuary, while their underside is white.
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Pleuronetiformes
Family: Paralichthidae
Genus: Paralichthys
Species: lethostigma
Taxonomy: Paralichthys lethostigma Jordan & Gilbert
This species has multiple names including Southern Flounder, flounder, fluke, and mud flounder.
This species is among the few flounder species that the right eye moves to the left side, while other flounders, halibut, and soles have the left eye that moves to the right side (Southern Flounder and Gulf Flounder, n.d.).
Another interesting fact about this species, the Southern Flounder female will disperse 17,000-100,000 eggs every three-seven days for two months (Southern Flounder and Gulf Flounder, n.d.).
Habitat
The Southern Flounder can be found from Albemarle Sound, North Carolina down to the Northeast of Florida in the Atlantic ocean, and from the Northwest of Florida to Mexico in the Gulf of Mexico. It is located within brackish estuaries, sometimes in rivers, and along the coastal ocean floor to about 40 m in depth (Froese, n.d.). Some reports have been made indicating the species is around Chesapeake Bay, Virginia. Adult males tend to live off the ocean floor, while females are frequently found in brackish waters of the estuaries.
The species can be found within the waters surrounding the Carolina Beach State Park.
Evolutionary History
The Southern Flounder has evolved to tolerate a salinity of 0-6%, and this is essential for the reproductive cycle. Southern Flounder spawn in coastal ocean waters during November - January. First the eggs grow into larvae, where it appears to be a typical fish with the eyes on either side. Then after about 30-60 days, the larvae settle to the bottom of the ocean floor to undergo metamorphosis into the juvenile stage. When complete, the juveniles swim and flow into the estuaries until sexual maturation, when males tend to move back to the ocean and females stay in the estuaries (Munroe, 2015).
The metamorphosis, an evolutionary adaptation, includes the movement of the right eye and the camouflage (Southern Flounder, n.d.). The chromatophores on the left side of the Southern Flounder move the pigment, melanin, to camouflage with the sandy and muddy ocean floor which allows the Southern Flounder to surprise prey and hide from predators (Southern Flounder and Gulf Flounder, n.d.). Additionally, the right eye moves to the left side of the fish when the "skeletal system, muscles, and nerves of the head gradually rearrange" which takes about two-three weeks (Southern Flounder and Gulf Flounder, n.d.). This metamorphosis allows the Southern Flounder to lay along the bottom of the estuary or ocean.
Environmental Impacts
The major ecological importance of the Southern Flounder is the species' distinction of being a top predator in the food webs of various coastal habitats (Southern Flounder, n.d.). The Southern Flounder controls the populations of various fishes and other species like shrimp and many invertebrates; furthermore, without this species, many fishes could overpopulate and in turn modify the estuary and ocean coast ecosystem.
Conservation
According to the IUCN Red List, the Southern Flounder is indicated as Near Threatened, according to the last assessment in 2015, due to the steady decreasing population caused by over-harvesting (Munroe, 2015). Although, one recent study has determined that the warmer water temperature could be causing more Southern Flounder to mature into males instead of females, which would drive down the reproduction cycle (Ford, 2019). Over-harvesting may not be the only cause for the rapidly decreasing Southern Flounder population.
North Carolina has introduced regulations on all flounder since 2013 by Amendment 1, in a way to help protect the fish industry as well as the fishes population.
- Recreational: Total Length minimum 15 inches
- Recreational: Creel Limit - 6
Then in 2017, North Carolina adopted Supplement A regulations.
- Commercial: Total Length minimum 15 inches
- Commercial: Gill net mesh size increased to 6 inches minimum
- Recreational: 4 flounder per person
Two proposed modifications that did not go into effect: annual closing of gill net season at Oct. 15 and reduction of harvest by 38%. (North Carolina Division of Marine Fisheries, 2019)
Since flounder populations have continued to decline, North Carolina Division of Marine Fisheries (2019) has introduced the proposed Amendment 2:
- Recreational Season: Aug. 16 - Sept. 30 (reel/gig)
- Commercial Season: Sept. 15 - Oct. 11
- Recreational Commercial Gear License: Sept. 15 - 30
- Overall coast wide, North Carolina to Florida, harvest reduction of 31%, 52%, or 72% (Rumley, 2019)
Friends and Foes
The Southern Flounder does not have many friends or foes. As a juvenile, it eats small fish, fish spawn, and invertebrates; as an adult, it eats shrimp, anchovies, pogies, and croakers (Biological Info: Southern Flounder, n.d.; Southern Flounder and Gulf Flounder, n.d.). Since it is well camouflaged, it is only eaten by predators such as sharks and dolphins; however, the Southern Flounder is the most commercially bought flounder in North America by humans.
Competition in North Carolina includes the two other flounder species, Gulf Flounder and Summer Flounder.
Videos
This video showcases a flounder's ability to camouflage to the surrounding mud and sand.
This video showcases the Southern Flounder's camouflage when eating prey.
Lesson Plan
IEE Lesson Plan 2.docxResources
North Carolina Division of Marine Fisheries Amendment 2 Draft - This is the proposed amendment to the regulations of flounder within North Carolina. It provides more detail in the proposed management strategies to help the Southern Flounder population.
IUCN Red List - This is the IUCN Red List website on the Southern Flounder, it includes various conservation efforts of states from North Carolina to Texas in detail.
Gulf Coast Research Laboratory - This website from The University of Southern Mississippi includes extensive information about the Southern Flounder as well as some information for the the Gulf Flounder.
Louisiana Fisheries - This site includes information regarding the Southern Flounder. This site contains an information list of facts about the Southern Flounder.
Southern Regional Aquaculture Center - This is a downloadable pdf file. This file contains a multitude of information for the Southern Flounder, although it is outdated.
References
Biological Info: Southern Flounder. (n.d.). Retrieved from https://www.seagrantfish.lsu.edu/biological/misc/southernflounder.htm
Burleson, J. (n.d.). Is it a summer, southern or gulf flounder? Retrieved from https://www.carolinasportsman.com/fishing/inshore-fishing/flounder/is-it-a-summer-southern-or-gulf-flounder/
Ford, D. (2019). N.C. Study: Warmer Water Linked to Higher Proportion of Male Flounder. Retrieved from https://news.ncsu.edu/2019/04/n-c-study-warmer-water-linked-to-higher-proportion-of-male-flounder/
Froese, R. (n.d.). Paralichthys lethostigma. Retrieved from Fishbase Database, https://www.fishbase.de/summary/981
Munroe, T. (2015). Paralichthys lethostigma. The IUCN Red List of Threatened Species 2015: e.T202632A46958684. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T202632A46958684.en.
North Carolina Division of Marine Fisheries. (May 2019). North Carolina Southern Flounder Fishery Management Plan Amendment 2 Draft [pdf]. Retrieved from https://files.nc.gov/ncdeq/Coastal%20Management/1-DraftSoFlAm2-2019-05-23.pdf
Rumley, V.S. (2019, February 20). Commercial, recreational flounder seasons could be in place by fall. Retrieved from https://www.thewashingtondailynews.com/2019/02/20/commercial-recreational-flounder-seasons-could-be-in-place-by-fall/
Southern Flounder. (n.d.). Retrieved from https://scaquarium.org/our-animals/southern-flounder/
Southern Flounder and Gulf Flounder. (n.d.). Retrieved from https://gcrl.usm.edu/public/fish/flounder.php