Fish and Shellfish Stocks 2012

WHITING STOCKS — WEST OF SCOTLAND

Whiting ( Merlangius merlangus) has not been a particularly valuable species and is primarily taken as a bycatch with other species. They are mainly caught by trawlers using gear with mesh size between 80 mm and 120 mm. Discarding of this stock remains high, particularly within the Nephrops fishery.

2012 position : UK share 176 tonnes
Last Year : 185 tonnes
Landed into Scotland in 2010 : 245 tonnes
Value for 2010 : £270,000

Biology

Whiting is widely distributed throughout the west coast of Scotland and high numbers of immature fish can be found in most sea lochs and inshore areas. The offshore stock is composed of older and larger fish which are recruited from the inshore shoals. Tagging experiments, and the use of fish parasites as markers, show that the whiting found to the south of 56°N and to the west of Ireland are separate from those in the Minches, the Clyde and the Irish Sea. The whiting population that overwinters in the Stanton Bank area moves to the Irish coast and the Clyde to spawn in spring. Some individuals may even move to the west of the Hebrides. There is no evidence to suggest movement between the west coast and the North Sea grounds.

Unlike some species, whiting do not form distinct spawning shoals, and both ripe and immature fish are often found together. As the latitude increases spawning of whiting occurs progressively later. This is closely associated with temperature changes, but spawning activity generally peaks in springtime, just as sea temperatures begin to rise. On the west coast of Scotland whiting spawn between January and June. Within this period, the spawning season of an individual female lasts around fourteen weeks, during which time she releases many batches of eggs. At two years old most whiting are mature and able to spawn. By the time it reaches four years old, a single female fish of reasonable size can produce more than 400,000 eggs. Like many other fish, whiting spend their first few months of life in the upper water layers before moving to the seabed. Male and female whiting grow very quickly reaching around 19cm in their first year. After this the growth rate becomes much slower. There are large differences between the growth rates of individual fish and a 30cm fish can be as young as one year or as old as six.

Whiting are active predators. Juvenile fish eat mainly crustaceans (shrimps and crabs) but as whiting grow, the amount of fish in their diet increases. The exact composition of the diet depends on the size of the fish, the area and the time of the year. Whiting is one of the main predators of other commercially important species of fish. Norway pout, sandeels, haddock, cod and even whiting themselves are frequently eaten. It has been estimated that each year the whiting population consumes several hundred thousand tonnes of these species.

ICES ADVICE ON MANAGEMENT

Information Source: ICES advice 2011 ( http://www.ices.dk/committe/acom/comwork/report/2011/2011/whg-scow.pdf). Quoted text in italics.

MSY and precautionary approach Reference Points

State of stock and advice

• Fishing mortality is uncertain. But estimates show it to have declined since 2005.
• The spawning stock biomass for 2011 is uncertain. But is estimated to be very low, although there are indications that recruitment increased in 2010.
• Fishing mortality and biomass cannot be determined with regard to either the Precautionary Approach or the transition to MSY Approach.
• The advice is based on the Precautionary Approach recommending that catches in 2012 should be reduced and that the selection pattern used by the Nephrops fleet be improved.

There is currently no specific management plan for this stock.

No reliable assessment can be presented for this stock. The main cause of this is due to historic uncertainties in the reported landings. However, based on the recent decline in trends of fishing mortality and the increased abundance of the 2009 year class, the stock would be expected to increase if the 2009 year class does not continue to be discarded at the rate observed in 2010.

There are strong indications that management control is not effective in limiting the catch. The proportion of fish discarded is very high and appears to have increased in recent years. More than half of the annual catch weight comprises undersized or low-value whiting which are discarded. 83% of these discards come from the Nephrops fishery. Measures to reduce discards and to improve the exploitation pattern would be beneficial to the stock and to the fishery, particularly when there are indications that the 2009 year class is relatively strong. Such measures should include the adoption of a sorting grid as well as appropriately located square-meshed panels.

Management outcomes for 2012

At the December 2011 meeting in Brussels, the Council of Ministers decided that the international Total Allowable Catch for west of Scotland (VI, EC waters of Vb and international waters of XII and XIV) whiting should be 307 tonnes. The UK quota for 2012 was set at 176 tonnes.

This quota decision was in line with the ICES advice to reduce catches.