Very little is known about the state of Turbot stocks in our area. They are a relatively rare species and landings to Cornish ports have decreased in recent years although this may be due to reduced fleet size. Discards of juvenile turbot is a problem in trawl fisheries.
Turbot are a large fast growing species of flatfish and a visual predator. They feed on a range of species of crustaceans and fish and can be described as a ‘top predator’. They can reach a size of around 30cm in just 3 years. They become sexually mature at this age and in most parts of its range spawns in April to August, females each producing up to 10-15 million eggs. Turbot can grow up to 1m in length and a weight of 25kg and can live for up to 25 years. Turbot are typically found at a depth range of 10 to 70m, on sandy, rocky or mixed bottoms. Turbot appears to be a rather sedentary species, although some adult migration may occur.
In our waters very little studies have been carried out so the size of the turbot stock is unknown. Landings data show that around 150 tonnes of turbot are caught each year although the landings have decreased from around 300 tonnes in 1994.(MMO data) (this may be due to reduced fishing effort and not an indication of size of stocks).
In the north sea where more studies have been carried out stocks are low but appear to be increasing slightly (ICES) and fishing pressure has reduced but even here there is not enough data to accurately predict the state of the stock. Seafish Ecological Risk Assesment for affects of fishing (ERAEF)score 3.9 – significant to major impact.
Turbot is a non-quota species and fishing effort is not limited. There is a minimum landing size of 30cm within Cornish waters. Turbot is a valuable by catch in trawl fisheries and gill net fisheries. The Sole recovery plan and the Trevose closure may help turbot stock.
Gill nets are monofilament nylon nets that are set on the seabed and left to fish. The size of mesh and the length of ‘soak time’ is specific to the species of fish being targeted. Local fisheries by laws govern mesh sizes within the Cornwall Inshore fisheries district and out side of the 12 mile limit EU regulations govern the allowable mesh sizes. By regulating the mesh size undersized or non-target species are more likely to escape capture.
There are however occasional issues with entanglement of non-target species such as pink sea fans and occasionally seals and cetaceans such as dolphins and porpoises. If nets become snagged on the seabed or get towed away by other fishermen they are lost. Lost nets can continue to fish and are termed ‘Ghost nets’. The length of time they are dangerous to wildlife depends on tidal flow and fishermen argue that strong current will roll the nets until they are no longer a threat but in practice this depends on many factors.
Project inshore pre assessment database
Seafish ERAEF 2014
Seafish Species guide Turbot