Whiting (Merlangius merlangus) is one of the smaller gadoid fish species that is of impoartance to Scottish Fishermen, caught using a variety of types of trawl and seine net. Whiting are caught all year round, mainly in mixed demersal fisheries with some bycatch taken in industrial fisheries. It is found throughout the North Sea, but is known to occur exclisvely in some localised areas. Disgarding of this species is still quite high on occasion.
There are two main stocks, the North Sea and the West of Scotland that contribute to North Sea landings. In 2011 7,431 tonnes worth £9.15 million were landed into Scotland by Scottish vessels.
Whiting is one of the most numerous and widespread species found in the North Sea. High numbers of immature fish occur off the Scottish coast, in the German Bight and along the coast of the Netherlands. Tagging experiments, and the use of a number of fish parasites as markers, show that the whiting found to the north and south of the Dogger Bank form two virtually separate populations. It is also likely that the whiting in the northern North Sea may contain populations including 'inshore' and 'offshore' groups. A separate population of whiting is widely distributed throughout the west coast of Scotland with immature fish occurring in sea lochs and inshore areas and older fish moving offshore. 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 over-winters 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.
At four years old, a single female fish of reasonable size produces more than 400,000 eggs. By two years old however, most whiting are mature and able to spawn. The spawning season lasts from late January until June. The spawning season of an individual female lasts 10-14 weeks, during which time she releases many batches of eggs. Like many other fish, whiting spend their first few months of life in the upper water layers before moving to the seabed. They grow very quickly for the first year, after which the growth rate becomes much slower. There are large differences between the growth rates of individual fish and a 30 cm fish can be as young as one year or as old as six. The whiting in the northern North Sea usually grow faster than their more southern counterparts.
Adult whiting feed mainly on juvenile fish and crustaceans (shrimps and crabs). The exact composition of the diet depends on the size of the fish, the area and the time of the year. In the North Sea, whiting is one of the main predators of other commercially important species of fish. Norway pout, sandeel, haddock, cod and even whiting themselves are frequently eaten. It has been estimated that each year, depending on the size of the whiting population, consumption of these species is of the order of a hundred thousand tonnes.
Whiting fishing mortality in 2010 was estimated to be 0.27: this means that approximately 24%, by number, of all fish aged between 2 and 6 years were caught. Spawning stock biomass (SSB) in 2011 was estimated to be approximately 205,000 tonnes. Fishing mortality and biomass cannot be determined in relation to the precautionary approach, as reference points have not been defined for this stock. There are no reference points to give advice on TAC's for the Maximum Sustainable Yield (MSY) or precautionary approaches.
West of Scotland
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.
For North Sea whiting, ICES considers that maintaining the level of fishing mortality at 0.3 would be consistent with long-term stability as long as recruitment is not poor. The EU and Norway adopted this level of fishing mortality for the interim management of the stock for 2011. ICES are in the process of developing and evaluating the management plan.
Whiting abundance estimations from surveys suggest that the northern component is declining, whereas the southern component is increasing or stable. The increase in the southern component is broadly in line with the industry's perception of the stock. Industry perceives increasing abundance of whiting in the northern North Sea but this is at odds with the evidence gathered from surveys.
However on the West of Scotland, there is currently no specific management plan for this stock as no reliable assessment can be presented at this time. The main cause of this is due to historic uncertainties in 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 high rates. 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. The majority 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.
At the December 2011 meeting in Brussels, the Council of Ministers of the EU set the Total Allowable Catches for whiting as follows:
North Sea 15,750 10,539
West of Scotland 307 176
None at present