Summer flounder

Paralichthys dentatus family

Paralichthyidae taxonomy

Pleuronectes dentatus Linnaeus, 1766, Carolina, United States. other common names

English: Fluke; French: Cardeau d'été; Spanish: Falso halibut del Canadá.

physical characteristics

Large, sinistral flatfish with a narrow, relatively elongate and thick body. Prominent head with a large terminal mouth with a wide gape and strong canine teeth on both jaws. A rounded or doubly emarginate caudal fin. Eyes are relatively large, separated, and nearly equal in position. Lateral line is arched above the pectoral fin. Scales are small and cycloid, with secondary squamation. Varies in coloration, as individuals change color to match the background of their habitat. Ocular side coloration ranges from drab olive-green to brown to gray; the blind side usually is white. Individuals captured on white sand are nearly completely white, whereas others on dark sediments can be nearly black. Some individuals have pink, green, orange, or brown coloration on the ocular side. The ocular side is marked variously with irregular spots, often with a series of more or less distinct ocelli that are slightly darker than the background coloration, with the most posterior of these arranged in a double triangle (one above and one below the lateral line). Males grow to about 24 in (61 cm) in length, with a weight of 5.7 lb (2.6 kg), and females grow to about 37 in (94 cm) in length, with a weight of 29.5 lb (13.4 kg). Most adults are 15.7-22 in (40-56 cm) in length and weigh between 2.2 and 5.1 lb (1.0-2.3 kg).

distribution

Western North Atlantic in estuarine and continental shelf waters of eastern North America from Nova Scotia to Florida.

habitat

Inshore waters, including estuaries and even freshwater (juveniles), bays, harbors, and the inner continental shelf. Summer flounder prefer sandy or muddy bottoms, where they often are found in sand patches near and within eelgrass beds or around pier pilings. Sensitive to low oxygen concentrations and will move out of hypoxic areas (less than 3 ppm oxygen). Concentrated inshore during warmer periods of the year, with smaller fish found in very shallow water. Larger fish in the northern part of the range occur farther offshore, usually at depths of 230-509 ft (70-155 m) and deeper, even during the summer. Estuaries are important nursery areas for this species. Young summer flounder can withstand a wide range of temperatures and salinity levels and are well adapted for estuarine life. Juveniles remain in estuaries until their second year of life in the southern part of their range, but to the north they move just outside them during winter. Many young fish return to the same estuary during their second summer.

behavior

Spend most of their lives on or close to the bottom. Occur most often on top of the sediment and do not ever bury deeply. Juve niles may be active at night, but adults appear to be most active during the daytime. Adults undertake strong seasonal inshore-offshore movements, especially in northern regions of the species' geographic range. Adults and juveniles are concentrated in shallow coastal and estuarine waters during the warmer months of the year and remain offshore in deeper waters (to about 492 ft, or 150 m) in the fall and winter, presumably to escape cold winter temperatures. Seasonal movements of summer flounder are complicated and are affected by fish size, location, and stock. Some may spend the winter in deeper bays and channels, and older fish may remain permanently on the outer shelf.

feeding ecology and diet

Diurnally active, opportunistic ambush predators. They feed while on the bottom but also rise off the bottom in pursuit of smaller fishes. The primary food of summer flounder is bony fishes, but cephalopods also are important prey of fish larger than 12.2 in (31 cm). Crustaceans, especially mysids and decapods, are important prey for smaller fishes (those fish less than 8.3 in, or 21 cm). Juveniles (3.9-7.9 in, or 10-20 cm) consume mysids, fishes, amphi-pods, and crabs. Feeding is most active during warmer periods and slows in winter. Spiny dogfish, blue sharks, skates, codfish goosefish, sea robins, bluefish, and winter flounder prey on summer flounder during various stages of their life history.

reproductive biology

Male and female summer flounder mature at about 9.8 in (25 cm) and 11 in (28 cm), respectively, corresponding to ages two and a half years for females and two years for males. Many fish may reach maturity at one year. Spawning occurs on or near the bottom, where temperatures range from 53.6 to 66.2°F (12-19°C), and usually takes place during the autumn migration to offshore wintering grounds on the outer continental shelf. Large females (more than 26.8 in, or 68 cm) may produce in excess of four million eggs during a spawning season. Females are serial spawners, continuously producing egg batches that are shed over a period of several months (September to March). Larvae are transported to coastal areas during winter and early spring by prevailing water currents. Post-larvae and young juveniles are found in or near the mouths of estuaries. Metamorphosis is completed within bays and estuaries, where young fish settle to the bottom.

conservation status

Not threatened. Exploitation of summer flounder by commercial and recreational fishers resulted in stock reductions throughout the species' range during the latter quarter of the past century. Fishery management plans have been developed to conserve and rebuild stocks by limiting commercial and recreational catches through size and season restrictions.

significance to humans

Summer flounder support the most important commercial and recreational fishery for flatfishes along the Atlantic coast of the United States. This highly prized game fish has strong fighting qualities and is excellent table fare. ♦

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