Common sole

Solea solea family

Soleidae taxonomy

Pleuronectes solea Linnaeus, 1758, European ocean. other common names

English: Dover sole; French: Sole commune; German: Seezunge; Spanish: Lenguado commune.

physical characteristics

Dextral flatfish with an elongate but rather thick body. The dorsal fin extends to the anterior part of the head, often to a point equal to a horizontal line drawn through the upper eye. Has a smoothly rounded head, projecting snout, and a small, subterminal mouth with small teeth and with the preopercu-lum covered by skin. On the blind side, head and snout are covered with close-set, whitish sensory papillae. Moderately large pectoral fins. On the ocular side this fin has a distinct elliptical black patch (not surrounded by white ring) on its upper extremity. On the blind side it is only slightly smaller than the ocular side counterpart. Last rays of the dorsal and anal fins are joined to the base of the caudal fin by a distinct membrane, and the last rays of the dorsal and anal fins overlap the bases of the caudal fin rays. Ocular side is uniformly dark brown or grayish brown, with numerous darker irregular blotches. Dorsal and anal fins are edged in white. Blind side is creamy white. Lengths reach about 27.6 in (70 cm) and weights about 6.6 lb (3 kg), but most fish are 11.8-15.7 in (30-40 cm) in length. They attain ages up to seven to eight years and perhaps older.

distribution

Northeastern Atlantic in estuarine and marine waters from off Norway and the western Baltic Sea and commonly off Ireland, England, and Scotland (uncommon northwest of Scotland). Also commonly along the European coast in the southern North Sea, the Mediterranean Sea, and the eastern Black Sea and southward to Senegal.

habitat

Occurs on soft sandy or muddy bottoms over a wide range of salinity levels and depths, ranging from shallow estuarine waters of 3.3 ft (1 m) or less down to about 656 ft (200 m). Estuaries are important nursery areas for newly settled fish and juveniles. Young-of-the-year soles appear in surf zone waters on shallow sandy beaches during summertime and can be taken even in shallow tide pools during this time. They occur at temperatures from 46.4 to 75.2°F (8-24°C). Adults and larger juveniles undertake seasonal migrations between shallower waters on the inner shelf (in warmer periods) to deeper areas (230-427 ft, or 70-130 m) on the outer shelf in winter. Larger fish generally are found in deeper waters than are smaller fish. Seasonal inshore migrations during springtime are complicated, because larger fish, besides moving inshore, also move toward definite spawning grounds. Young fish move into inshore waters earlier, usually during spring, whereas larger fishes move into shallower waters by late spring or early summer.

behavior

Benthic fishes that live somewhat solitary lives. They spend much of the daylight hours partially buried in sediments or lying on top of them. In overcast conditions or in turbid waters, such as in estuaries, they are more active during daylight hours. Generally, they are most active at nighttime, when they sometimes are found off the bottom and up in the water column. They are found pelagically during migrations.

feeding ecology and diet

Opportunistic, nocturnal feeders that rely on chemosensory and tactile information to locate their prey. Some feeding by adults and juveniles also takes place during daylight hours when fish are active. In some estuaries, feeding activity showed a strong relationship to the tidal cycle. Juveniles may use intertidal areas as feeding grounds during flood tides. They consume a diverse array of mostly benthic prey, including amphipods, polychaetes, oligochaetes, small bivalve mollusks and siphons of bivalve mollusks, gastropod mollusks, mysids and crangonid shrimps, brittle starfish, and, to a lesser extent, small benthic fishes, such as sand eels (Ammodytes) and gobies. Diets often vary between habitats and in terms of size of fish, with prey sizes generally increasing with increasing fish size. Soles feed on small quantities of prey very often. Predators of sole include spiny dogfish, hakes, lizardfish, codfish, weaver fish, and cormorants.

reproductive biology

Mature at three to five years of age and at sizes of about 9.1-11.8 in (23-30 cm). Spawn primarily during one well-defined season in the spring and early summer, which varies according to latitude (March to May off England and April to June farther north). Spawning grounds are located in both shallow and deep waters. Spawning takes place between 42.8 and 53.6°F (6-12°C). Females may release up to 100,000 eggs during a spawning event. Eggs are buoyant and pelagic; planktonic larvae hatch when eggs reach a length of about 0.12-0.16 in (3-4 mm). Metamorphosis occurs at about 0.47-0.59 in (12-15 mm), with settlement taking place at 0.59-0.7 in (15-18 mm) in length. Adults undertake migrations to definite spawning grounds located on the inner continental shelf at depths of 131-197 ft (40-60 m). Spawning grounds have been identified in the North Sea, the Irish Sea, and the English Channel.

conservation status

Not threatened. Stock sizes have been reduced owing to over-fishing. At present, efforts have focused on limiting fishing pressure and reducing mortalities, with expectations that stock sizes will not decline further.

significance to humans

Abundant and valued food species. The most valuable fishing grounds lie in the southern and central North Sea and the Bay of Biscay. Little recreational fishing occurs, primarily because of this species' nocturnal feeding habits and also because of the difficulty in catching it. ♦

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