Plaice
Plaice can be distinguished from the other species of flatfish by the orange specks on the side of the animal where the eyes are. It lives on the seabed where it preys mainly on molluscs and worms. Plaice spawns in the southern North Sea. After the eggs hatch, the larvae are carried with the sea current and the young fish eventually float into the food-rich tidal regions, where they remain until adulthood. An adult plaice can grow to 80 centimeters. Together with sole, plaice is one of the most important sources of income for the Dutch fisheries.
Distribution and reproduction
Plaice is a typical coastal fish of the North Atlantic Ocean.
| In January-February, the females lay around a half million eggs in the spawning grounds at sea. The eggs hatch there as well, but the larvae are carried with the tidal current to the Wadden Sea and a few other coastal regions, where they spend their first years of life. They look for food in the flooded mud flats during high tide, where they eat all kinds of benthic animals. One-year old plaice eat mostly the siphons of Baltic tellins. They eventually switch over to the tails of lugworms, which are more difficult to catch. After three years, when the fish has reached a length of around twenty centimeters, it leaves the Wadden Sea to spend the rest of its life in the North Sea. | 
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It has been established that without the Wadden Sea, the percentage of plaice fished up in the North Sea would be considerably less. 75% of the plaice in the North Sea grow to adulthood in the Wadden Sea.
Plaice migrate in severe winters to places where the sea remains warm. This migration is less explicit than the warm water migrations of sole, but plaice can also be easily caught in the deeper parts of the southern North Sea in severe winters.
A British research team marked plaice around 1995 with electronic equipment in order to register its migrating behaviour. Their data showed that plaice can travel much larger distances than had been assumed. One plaice had travelled 900 kilometers within 56 days, from the eastern coast of the English Channel to the Flamborough Off Ground and back again. For this kind of long voyage, the plaice make use of tidal currents: it swims to the upper water layers with a current flowing in the favourable direction; when the current turns, the plaice drops to the bottom and waits till the next change.
Development of the plaice stock
The plaice catch in the North Sea reached a record high of approximately 150,000 tons per year around 1987. Since then, the haul has gradually declined to 56,000 in 2005. The fishery death (partially due to by-catch) has increased to around 40% of the total amount. The adult (spawning) stock varied in the past between 300,000 and 500,000 tons, however has been decreasing since 1989 from 419,000 to around 189,000 in 2004. This is the lowest spawning level since 1957 and far below the biological minimum of 230,000 tons considered safe by the fishery biologists since 2004.
Of the total amount of plaice which the Dutch beam trawlers fish in the North Sea, 80 to 90 percent come from the coastal zone between Texel and Denmark. The remaining 10 to 20 percent, originating mostly from the Danish section of the nursery, swim in the northern North Sea.
Plaice fisheries
Plaice can be fished in many ways. Most plaice in the North Sea are caught with beam trawls containing tickler chains. Twinrigging, electro-fishing and sumwing are fishing methods that cost much less energy and can result in good plaice yields. The Danish coastal fleet catches plaice with purse-seining. Plaice is the traditional specialty for the large cutter fleet in Urk. The majority of the yield is exported as frozen filet.
Since 1 January 2008, a long-term management plan for North Sea plaice (and sole) was established by the European Community. This plan includes decreasing the fishery pressure on plaice by 10% every year, until the plaice population has grown above safe levels.
For a long time, there were discussions whether plaice should be caught during periods when the females carry roe. That period is roughly the months January till March. This ‘roe-stage’ plaice looks less appetizing than normal plaice, but the greatest advantage of course is that the females provide more offspring when given the chance to spawn. The discussion was settled in 2007 when two large supermarkets in the Netherlands decided not to sell fresh plaice during the spawning period. Therefore, the cutter sector decided to strongly limit plaice catches in the first three months of the year.
Protecting nurseries
 | In order to better protect young, undersized plaice, a plaice box was established in 1989. This region, around 40,000 square kilometres north of the Dutch and German Wadden Islands and west of the Danish Wadden Islands, is closed the entire year to beam trawlers with a motor capacity greater than 300 hp. |
Plaice sexually mature earlier due to fisheries
In the 1950s, female plaice were sexually mature between the lengths of 27 to 41 centimeters, at an age between three and seven years old. Because the fisheries have removed the large plaice, smaller plaice have more chance to produce young. The female specimen turn adult earlier due to the selection pressure from the fisheries, now between a length between 25 and 37 centimeters. Norwegian studies have shown that cod found along the Canadian coast also show this trait: females become sexually mature at an earlier age and remain smaller.
Names:
Dut: Schol (bunscholleke, kantschol, keu, kraat, plaat, pladijs, ronde schol, spreischol)
Lat: Pleuronectes platessa
Eng: Plaice
Ger: Scholle, Goldbutt
Fren: Plie, Carrelet
Dan: Rødspætte
Source: de Vleet, Ecomare
