Plaice

Scientific: Pleuronectes platessa. English: Plaice, European plaice. Icelandic: Skarkoli, rauðspretta. For more languages see the Marine Animal Dictionary.

Biology and distribution

Plaice is a medium sized flatfish. It has a smooth skin as opposed to, for example, dab and long rough dab. It is easily recognized by the red or orange spots on the otherwise dark back, the underside is white. The maximum recorded size in Icelandic waters is 85 cm, but the usual size in catches is from 30 to 50 cm. Plaice is common all around Iceland from the seashore to 200 m depth, on sandy or muddy bottoms. It can also tolerate fresh waters for some time. In European waters it is found from the White Sea and the Barents Sea in the north down to the western part of the Mediterranean Sea in the south. It is not found in North American waters. Previously, flatfishes were considered rather sedentary. Tagging studies on the plaice have, however, shown that this does not hold entirely true. The plaice undertakes large scale feeding and spawning migrations in the waters around Iceland, fishes tagged on one side of the country have even found at the other side.

Spawning mostly takes place in the warmer waters south and west of Iceland at 50 to 100 m depth. Eggs and larvae have also been found in colder northern waters, so at least some limited spawning also occurs there. In the southern waters, the peak spawning season is in March and April but in May and June in northern waters. The juveniles settle onto shallow intertidal beaches and stay there for the first year of their life before migrating to deeper waters.

Plaice is relatively fast growing and can reach a larger size than other flatfish species in Icelandic waters, with the exception of halibut and Greenland halibut. Females grow larger than males as is common with flatfishes. Growth is, however, quite variable and has been shown to depend on temperature, food abundance and stock size, among other things. The plaice reaches 50% maturity at around the age of 5, maximum age being more than 20 years. Plaice feeds mainly on various benthic invertebrates, dominated by polychaetes and bivalves, but also, to some extent, on small fishes such as sandeels.

Catches and fishing methods

Because of its good taste, abundance and shallow water distribution, plaice has sustained high catches in Icelandic waters since the beginning of the trawler age. Catches have usually been similar or higher than for all other flatfish species combined. Originally, the bulk of the catches were by British trawlers, but, for the last decades, have been exclusively by Icelandic boats. Catches have been in the general range of 5,000 to 10,000 tons per year since the beginning of the 20th century. Most of the current catches are by Danish seine, but a considerable share is taken by bottom trawl. Catch by other fishing gear is neglegible. The major fishing areas are off the south west and west coasts.

Stock status (from the Marine Research institute)

In 2010, 6 000 t of plaice (Pleuronectes platessa) were landed, a decrease of 300 t from 2009. Survey indices have increased somewhat in recent years, and recruitment measurements from the groundfish survey suggest some improvement in the last few years. Stock assessment results show increasing biomass since 2000 and fishing mortality has also been decreasing since then. The MRI recommends that the catch should not exceed 6 500 t in the quota year 2011/2012, and that regulations regarding area closures on spawning grounds remain in effect.

Processing and markets

The majority of the Iceland catch is either iced at sea and then processed and frozen in Icelandic factories or in equal amounts exported fresh in containers. An increasing share is also exported fresh by air. Plaice is one of the most popular food fishes in Northern Europe, especially in the United Kingdom and Denmark. More than 95% of the Icelandic catch is exported to the United Kingdom, the fillet being commonly eaten fried or battered and deep-fried in fish and chips.

References and further information

References: (Pálsson, 1983), (Hjörleifsson & Pálsson, 2001), (Sigurðsson, 1982), (Sólmundsson, Karlsson, & Pálsson, 2003), (Sólmundsson, Pálsson, & Karlsson, 2005), (Jónsson & Pálsson, 2006).

For full citation and further information on the main species in general see this page

Hreiðar Þór Valtýsson, University of Akureyri