Winter Flounder (Pseudopleuronectes americanus)

• According to the most recent stock assessment, winter flounder stocks suffered moderate declines since the last assessment in 2004.
• Winter flounder declined for decades and are now tightly managed under state and federal fishery management plans.
• Flounder is a good, low-fat source of B vitamins and an excellent source of niacin. For more on nutrition, see Nutrition Facts. (USDA)
• Winter flounder are one of the five flounders most commonly found on dinner tables.

Sustainability Status

Biomass: Georges Bank is 31% of the biomass needed to support maximum sustainable yield (B_MSY). Southern New England/Mid-Atlantic is 9% of B_MSY. The most recent biomass estimates for the Gulf of Maine stock are highly uncertain but are believed to be below sustainable levels.
Overfishing: Yes (Georges Bank, Southern New England/Mid-Atlantic); No (Gulf of Maine*)
Overfished: Yes (Southern New England/Mid-Atlantic); No (Gulf of Maine*, Georges Bank**)
Fishing and habitat: Winter flounder is mainly caught in the commercial fishery by otter trawls. Otter trawls can have a negative impact on benthic habitat, the severity of which depends on the type of particular habitat (e.g., sandy, rocky, stable, subject to frequent natural disturbance, etc).
Bycatch: Otter trawls catch a variety of species and sizes of fish, depending upon their mesh size and method of use. Therefore, vessels targeting winter flounder may catch other species, and vessels targeting other species may catch winter flounder.
Aquaculture: There is currently no commercial aquaculture of winter flounder in the U.S., but research indicates that the species is an excellent candidate for stock enhancement. Scientists know how to raise them, and current research is focusing on maximizing their survival in the wild and understanding their impact on the wild population.

*The Gulf of Maine stock is currently considered not overfished and not subject to overfishing. However, the results of the latest stock assessment (published in September 2008) do not give a clear picture of the status of the stock. It is generally believed that biomass is now below the target level.
**The Georges Bank stock is currently considered subject to overfishing but not overfished. However, based on results from the most recent stock assessment (published in September 2008), the stock may be considered overfished if the results are finalized.

Science and Management

U.S. commercial and recreational fisheries for winter flounder are managed in federal waters under the New England Fishery Management Council's (NEFMC) Northeast Multispecies Fishery Management Plan (FMP) and in state waters under Atlantic States Marine Fisheries Commission's FMP for Inshore Stocks of Winter Flounder. The two authorities cooperate in the management of this resource because winter flounder migrate from federally-managed offshore habitats to state-managed inshore habitats to reproduce. Management measures include restrictions on commercial permits, limits on commercial fishery days-at-sea, commercial and recreational fishery time-area closures, commercial fishery mesh sizes, commercial and recreational fishery fish size limits, and commercial and recreational fishery possession limits. Inshore habitat degradation and overfishing led to serious stock declines throughout the species' range, but efforts of the Atlantic coastal states and the NEFMC to reduce fishing mortality and identify essential habitat have allowed stocks to begin to recover.

Life History and Habitat

Life history, including information on the habitat, growth, feeding, and reproduction of a species, is important because it affects how a fishery is managed.

• Geographic range: Winter flounder are found in the Northwest Atlantic from Labrador to Chesapeake Bay.
• Habitat: Young-of-the-year (fish born in the past year) and some one year-old fish remain in the estuaries where they were hatched throughout the year. Juveniles prefer sand or sand-silt bottoms in a wide range of salinity and temperature. Adults occupy bottom habitats in inshore bays and estuaries during the winter and deeper water in the summer. While inshore, adults prefer muddy sand, clean sand, clay, and pebbly or gravelly ground.
• Life span: 15 to 20 years.
• Food: Adults feed on small invertebrates, shrimp, clams, and worms.
• Growth rate: Growth varies by stock - Georges Bank winter flounder grow the fastest, and Gulf of Maine grow the slowest.
• Maximum size: Up to 1.9 feet total length. Georges Bank winter flounder are the largest; Gulf of Maine are the smallest.
• Reaches reproductive maturity: Maturity varies by stock - Georges Bank winter flounder reach maturity at the earliest age and smallest size, and Gulf of Maine reach maturity at the oldest age and largest size.
• Reproduction: Females usually produce between 500,000 and 1.5 million eggs, but up to 3.3 million eggs have been reported. Females deposit eggs on sandy bottoms and algal mats at night. This event occurs an average of 40 times per spawning season. Proper temperature and salinity are critical to the survival of eggs during larval development. Five to six weeks after hatching, larvae settle to the bottom to begin metamorphosis. After eight weeks, the left eye migrates to the right side of the body and metamorphosis is complete.
• Spawning season: During the winter and spring.
• Spawning grounds: Winter flounder spawn in shallow inshore waters. Adults tend to return to the same spawning grounds every year.
• Migrations: Every January, winter flounder migrate from offshore areas where they feed to inshore areas where they spawn.
• Predators: Fish, such as striped bass, bluefish, toadfish, and summer flounder, birds, invertebrates, and marine mammals prey on larvae and juveniles. Atlantic cod, spiny dogfish, monkfish, and winter skate prey on adults. Smooth dogfish, hakes, sea raven, striped sea robin, striped bass, bluefish, and wrymouth also eat adults but in smaller amounts.
• Commercial or recreational interest: Both
• Distinguishing characteristics: Winter flounder can be identified by eyes on the right side of the body, a straight lateral line, and dark coloring. Coloring often varies with habitat; it ranges from muddy to slightly reddish brown, olive green, or dark slate, to an almost black upper. Their underside is white, and their dorsal and anal fins are often tinged with pink, red, or yellow on the eyed side.

Role in the Ecosystem

In the ecosystem, the winter flounder is a part of the complex food web, contributing to the diversity of the continental shelf ecosystem. Winter flounder are limited in the scope of their diet by their relatively small mouth size and eat a variety of small invertebrates. They are mainly preyed upon by cod, spiny dogfish, monkfish, and winter skate.

Additional Information

Market names: Flounder or Sole
Vernacular names: Winter Flounder, Lemon Sole, Georges Bank Flounder, Blackback Flounder

Biomass

Biomass refers to the amount of winter flounder in the ocean. Scientists cannot collect and weigh every single fish to determine biomass, so they use models to estimate it instead. These biomass estimates can help determine if a stock is being fished too heavily or if it may be able to tolerate more fishing pressure. Managers can then make appropriate changes in the regulations of the fishery. In the U.S., the resource is assessed and managed as three stocks: Gulf of Maine, Georges Bank, and Southern New England/Mid-Atlantic Bight.

Gulf of Maine winter flounder is the smallest of the three winter flounder stocks. The stock was most recently assessed in 2007, and results of this assessment are highly uncertain. Spawning stock biomass (SSB) was estimated to be 1,100 metric tons, about 29% of the SSB needed to support maximum sustainable yield, so the stock is likely to be overfished.

Georges Bank SSB declined rapidly from a peak of 16,300 metric tons in 1982 to 5,573 metric tons in 1985. SSB increased slightly through 1987 to 7,519 metric tons but declined again to a low of 3,226 metric tons in 1994. SSB again increased to 10,924 metric tons in 2000 but then declined to 4,478 metric tons in 2005. In 2007, Georges Bank spawning stock biomass increased slightly to 4,964 metric tons, still well below the target of 16,000 metric tons, indicating that the stock is overfished.

Southern New England/Mid-Atlantic SSB declined from 14,714 metric tons in 1983 to a record low of 2,098 metric tons in 2005. SSB increased to 3,368 metric tons in 2007, about 9% of the target SSB of 38,761 metric tons, so the stock is currently overfished.

Landings

Landings refer to the amount of catch that is brought to land. In the Gulf of Maine, commercial landings were near 1,000 metric tons from 1964 to the mid 1970s. They then increased to a peak of 2,793 metric tons in 1982 but steadily declined to 350 metric tons in 1999. Commercial landings were near 500 metric tons from 2000 to 2004 and declined to a record low of 200 metric tons in 2006. 2007 landings remained low at 260 metric tons.

In Georges Bank, total commercial landings are predominately from the U.S. bottom trawl fleet, but some landings from the area have also been reported in the Canadian groundfish trawl fisheries. Total commercial landings increased from 1964 to 1972, peaking at 4,509 metric tons in1972. They then declined to 1,892 metric tons in 1976. Higher landings occurred from 1977 to 1984, ranging from 3,061 to 4,009 metric tons, but after 1984, landings gradually declined to 783 metric tons in 1995. They increased again to 3,139 metric tons in 2003 but declined rapidly thereafter and reached in the lowest level on record in 2007 (787 metric tons).

In Southern New England/Mid-Atlantic area, commercial landings reached a historical peak of 11,977 metric tons in 1966. They then declined through the 1970s, peaked again at 11,176 metric tons in 1981, but steadily declined to 2,128 metric tons in 1994. Commercial landings increased to 4,556 metric tons in 2001 before falling to a record low of 1,320 metric tons in 2005. Commercial landings were 1,622 metric tons in 2007.

Note: U.S. commercial landings are shown in the graph.

Biomass and Landings

Are landings and biomass related? Landings are dependent on biomass, management measures in the fishery, and fishing effort.

Data sources:
Biomass and landings from Northeast Fisheries Science Center Assessment of 19 Northeast Groundfish Stocks

Important Dates

1986 – Northeast Multispecies Fishery Management Plan implemented to reduce fishing mortality and promote rebuilding
1992 – Atlantic States Marine Fisheries Commission's (ASMFC) original winter flounder FMP is implemented
2004 – Amendment 13 to the Northeast Multispecies FMP implements days-at-sea reductions and restrictions to reduce fishing mortality on the Southern New England/Mid-Atlantic Bight stock
2005 – Amendment 1 to the ASMFC's FMP is implemented

Notes and Links

General Information:
Northeast Fisheries Science Center Status of Fishery Resources off the Northeastern U.S. - Winter Flounder

Essential Fish Habitat Source Document - Winter Flounder

NMFS Sustainability Species Identification - Winter Flounder

Atlantic States Marine Fisheries Commission - Winter Flounder page

New England Fishery Management Council - Winter Flounder page

Fishery Management:
Northeast Multispecies Fishery Management Plan

Summary of Northeast Multispecies Fishery Management Plan

Northeast Multispecies FMP Plan Amendments

Northeast Multispecies FMP Plan Adjustments

Stock Assessments:
Northeast Fisheries Science Center Assessment of 19 Northeast Groundfish Stocks through 2007