Turbot

(Psetta maxima)

Order: Pleuronectiformes Family: Scophthalmidae

Fotos: Jussi Pennanen

Description: The body of the turbot is flat and almost as round as a plate. It has a large mouth, and a dark brown mottled skin covered in tubercles on the upper side. The underside is a pale creamy colour and almost always smooth.

Origin and distribution: The turbot occur in almost all coastal waters of Europe and North Africa. In the Baltic Sea it is to be found from the sounds of Denmark to the Gulf of Finland and the Gulf of Bothnia, though it becomes less common toward the heads of the gulfs. The turbot is a typical species of temperate sea areas, and cannot reproduce in very low water salinity. Finland's coast is at the extreme limit of its range, so even in favourable environments it accounts for no more than 10% or 20% of the two flatfish species occurring in Finland.

Reproduction: Turbot spawn in shallow, coastal waters, at a depth of 2–8 m, towards the end of June. The eggs are pelagic if the salinity is at least about 8‰. To start with, the hatched larvae are planktic and their eyes are normally on both sides. By the end of their first summer, however, when descending to the bottom, they go through a metamorphosis and start to resemble adults, with both eyes on the upper (left) side. They usually reach a length of 3−6 cm before their first winter.

Diet, growth and migrations: The turbot has a diverse diet comprising bivalves, crustaceans and fish. It has a large mouth with many small, sharp teeth, which are useful for the predator into which the turbot invariably develops with age. In the Baltic Sea, the growth rate of the turbot is clearly slower than it is in the oceans, yet still faster than that of the flounder. Turbot caught off the Finnish coast are usually 20−40 cm in length and 0.5−1 kg in weight, though individuals weighing as much as 2 kg are caught fairly regularly. In the ocean their weight may even exceed 20 kg. A turbot weighing almost 6 kg caught in the Kustavi area in 1994 is probably the biggest ever caught in Finland. Like the common flounder, the turbot may live long, even 15−16 years. The turbot is a local species, and during its short migrations actually only moves between breeding, feeding and over-wintering areas, all of which are situated relatively close to one another.

Fishing and catches: Turbot have little economic significance in Finland because of their low numbers. On the European side of the Atlantic, they are caught with trawls and drift nets, usually as a by-catch. In Finnish coastal waters, they can be caught using hooks or large mesh nets, but the annual catch is small.

Vulnerability, threats and management: Turbot stocks are heavily dependent on changes in water salinity and on other water quality factors.

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