Turbot is taken as a valuable bycatch in flatfish fisheries for plaice and sole. There is a general absence of stock data for turbot, insufficient to evaluate stock status. Available information suggests the North Sea stock biomass, where 90% of the catches in the Northeast Atlantic are taken, is now increasing but from a low level.
Turbot belongs to a small family of left-eyed flatfish (both eyes on the left of the body), known collectively as the Scophthalmidae. This family of fish is confined to the North Atlantic basin and includes megrim and brill. Turbot becomes sexually mature at an age of 3-5 years, and in most parts of its range spawns in April to August, females each producing up to 10-15 million eggs. Turbot is one of the fastest growing flatfish with females growing faster than males, in the North Sea reaching a length of c. 30cm (males) and 35cm (females) in about 3 years. In the Baltic Sea growth is slower, and the males become sexually mature at a length of 15cm, the females at 20cm. By 10 years of age growth rates have reduced to 1-2cm per year for females and less than 1cm per year for males. Consequently, females are larger than males at any given age. Turbot can attain a length of 1m and a weight of 25kg. Maximum reported age 25 years. For some reason males are generally more abundant than females. Turbot is distributed from Iceland, down the coast of western Europe and into the Mediterranean. Turbot are typically found at a depth range of 10 to 70m, on sandy, rocky or mixed bottoms. It is one of the few marine fish species that inhabits brackish waters. Turbot appears to be a rather sedentary species, although some adult migration may occur.
ICES indicate that there are distinct turbot populations in the Baltic and Irish Sea. There are also indications that turbot from the North Sea, the southern coast of Iceland, the western coast of Scotland and Ireland, and the Celtic Sea (including the Western Approaches) forms another (North Atlantic) stock, which differs from the Bay of Biscay and southern European Atlantic stock. This species is not formally assessed by ICES, but instead is considered by the ICES Working Group on the Assessment of New MoU Species (WGNEW). Available information suggests North Sea stock biomass is now increasing from a low level, and fishing mortality has decreased in recent years, probably as a consequence of decreased beam trawl effort directed toward the target species of plaice and sole. In 2015 ICES advises that catches in the North Sea should be no more than 2,406t (2,978t in 2014).
No specific management objectives are known to ICES. An EU total allowable catch (TAC) is set for EU waters of ICES Division IIa and Subarea IV together with brill. ICES suggests TACs may not be an appropriate management tool for bycatch species such as turbot. Turbot is currently under consideration by the ICES Working Group on the Assessment of New MoU Species (WGNEW). There is almost no relevant fisheries data for this species from any of the areas in which it is fished. Low representation in catches is cited as problematic for the collection of some types of data. ICES recommends increased data collection for this species to enable fishery trend evaluation and advice in future, including upgrading brill to Group 1 (compulsory annual data collection, and market sampling).
Turbot is a valuable bycatch species in beam and otter trawl (90%) and gillnet (10%) fisheries for flatfish (plaice and sole) and demersal species. Quota restrictions apply only to the North Sea, where 90% of the catches in the Northeast Atlantic are taken, and where they are included in a quota with brill. There is no official EU minimum landing size, although Minimum Landing Sizes (MLS) have been introduced by different authorities. The most frequently applied MLS is 30cm (e.g. Belgium, Baltic, Cornwall).
ICES Advice 2014, Book 6 http://www.ices.dk/sites/pub/Publication%20Reports/Advice/2014/2014/tur-nsea.pdf
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