Winter Flounder (Pseudopleuronectes americanus)

• Winter flounder populations are rebuilding. The Gulf of Maine and Georges Bank stocks are no longer considered overfished.
• 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: Gulf of Maine and Georges Bank biomass estimates have improved the most and are 84% and 66% of the biomass needed to support maximum sustainable yield (B_MSY). Southern New England/Mid-Atlantic biomass is still quite low at only 13% of B_MSY.
Overfishing: No (Gulf of Maine); Yes (Georges Bank and Southern New England/Mid-Atlantic)
Overfished: No (Gulf of Maine and Georges Bank); Yes (Southern New England/Mid-Atlantic)
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.

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 Georgia.
• 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. When offshore, adults inhabit hard bottoms.
• 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.
• Predator/prey interactions: 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. Little skate, 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, Southern New England/Mid-Atlantic Bight, and Georges Bank.

In the Gulf of Maine, biomass indices began to decline after 1983, reaching a record lows in 1986 (fall survey) and 1994 (spring survey). Between 1996 and 2000, both survey indices increased. The 2000 spring index was the highest on record and the 2000 fall index was the 2nd highest in the 28-year time series. However, the indices have since declined. Spawning stock biomass declined from 4,800 metric tons in 1982 to 500 metric tons in 1996 and then increased to 3,400 metric tons by 2004.

The Georges Bank stock declined between 1976 and 1991. Thereafter, biomass increased through 2002, then declined to a level near the time series average in 2005.

The Southern New England stock peaked in abundance during the mid-1960s, early 1980s, and late 1990s, but has generally declined since 1999. Spawning stock biomass declined from 14,800 metric tons in 1983 to 2,700 metric tons in 1994, slowly increased to 5,000 metric tons in 2001, and has since stabilized at about 4,000 metric tons.

Note: Biomass indices from the Northeast Fisheries Science Center's fall survey are presented in the graph.

Landings

Landings refer to the amount of catch that is brought to land. In the Gulf of Maine, commercial landings increased from an annual average of about 1,000 metric from 1964 to 1975 to nearly 3,000 metric tons in 1982. Commercial landings have since declined to 300 metric tons in 2005. The recreational fishery historically harvested a significant proportion of the total landings, but catches have sharply declined from over 2,500 metric tons in the early 1980s to less than 100 metric tons during 1997-2005.

Commercial landings of Georges Bank winter flounder are predominately from U.S. fisheries, but a small percentage (less than 12% during most years) is from Canadian fisheries. After reaching a peak of 4,500 metric tons in 1972, total landings of Georges Bank winter flounder declined to 1,900 metric tons in 1976. From 1977 to 1984, total landings ranged between 3,000 and 4,000 metric tons, but thereafter declined to a record low of 800 metric tons in 1995. Total landings increased between 1995 and 2003 then declined to 2,200 metric tons in 2005.

In Southern New England and the Mid-Atlantic Bight, U.S. commercial landings of peaked at 12,000 metric tons in 1966, declined through the 1970s, and then peaked again at over 11,000 metric tons in 1981. Commercial landings subsequently declined during the 1980s and early 1990s, falling to 2,200 metric tons in 1994. Commercial landings then increased to 4,700 metric tons in 2001 but have since declined to a record low of 1,200 metric tons in 2005. The recreational fishery historically harvested a significant proportion of the total catch, but recreational landings have declined considerably from a peak of 5,800 metric tons in 1984 to 120 metric tons in 2005.

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 Status of Fishery Resources off the Northeastern U.S. - Winter Flounder

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:
2005 Groundfish Stock Assessments