Saithe (Pollachius virens) or Coley as they are often called in Scotland; are mainly taken by demersal trawl as part of a directed fishery by French, German and Norwegian fishing fleets, along the Northern Shelf edge and Norwegian Trench. Some Scottish vessels target saithe but they are mostly caught as a species component of Scottish demersal mixed fisheries. They are caught in the northern North Sea, to the west and north of Shetland on the Northern shelf edge and on the southern and western limits of the Norwegian Trench. They are, by weight, the second most landed round fish species caught by Scottish demersal fishermen.
In 2010 the UK fleet landed over 13,500 tonnes of saithe into Scotland with a value of approximately £12.29 million. Despite it's cod-like qualities, saithe remains underutilised in the UK, most of this species is exported to northern EU countries.
Adult saithe can be caught in almost any sea area but occur mainly around the 200m depth contour. In late summer and autumn young saithe are found in large numbers within Scottish and Norwegian coastal waters, usually on grounds which are unsuitable for commercial fishing. The adult stock can occur in dense shoals which move around the water column and are often caught hundreds of metres above the seabed.
Saithe reach maturity between the ages of four and six years. A medium sized adult female can produce about 2.5 million eggs during a spawning season. Spawning takes place between January and April near to the edge of the continental shelf to the north and west of the Outer Hebrides. Initially the young fish live near to the surface but by mid-summer they can be found close inshore, in bays and harbours. In their second year they live along the shoreline before eventually moving to deeper water. This offshore migration usually occurs in springtime. Saithe grow quickly, averaging around 15cm per year for the first three years and 10cm for the next three, reaching 100cm by the time they are eleven years old.
Saithe are active predators, feeding on the bottom and in mid-water. By weight, fish prey dominate their diet at all times of the year. Herring, Norway pout and sandeel are the main fish species eaten.
Fishing mortality (F), has generally increased since 2004 and is currently just below the precautionary reference point Fpa. The status of the stock has deteriorated in the last few years. The spawning stock biomass is estimated to have been above the precautionary reference point Bpa from 2001–2008 but has since declined to just below Bpa. Fishing mortality and biomass are both below their precautionary limits. However fishing mortality is above the level which is consistent with achieving maximum sustainable yield.
There has been a southern shift in geographical distribution in fishing pattern, at least for the German fleet. This is probably due to EU fleets coming under the effort regime of the EU cod management plan, and may shift the distribution of catches toward younger fish. Due to these changes in fishery distribution and stock productivity (lower growth and recruitment) a re-evaluation of the management plan for saithe stocks is needed. The re-evaluation is envisaged for 2012.
At the December 2011 meeting in Brussels, the Council of Ministers of the EU set the Total Allowable Catches for saithe as follows:
West of Scotland
and North Sea 87,550 9,472
None at present.