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.

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.

Plaice fishing grounds in 2007 (tonnes/nm2). All gear combined. Dark areas indicate hihghest catches.

Source: The Marine research Insittute

The lemon sole is a medium sized rather thickset flatfish, usually around 30 cm long, but the largest individual caught in Icelandic waters measured at 63 cm. It is found all around Iceland, but is much rarer in the colder waters north and east of the country. Mostly it occurs on rocky or sandy bottoms at depths between 50 to 350 m. It is found in European waters from Murmansk in the north to the Bay of Biscay in the south. Also around the Faroe Islands, in Greenlandic waters and from Labrador to Cape cod in North America.

Lemon sole feeds primarily on polychaetes, but also to a lesser extent on other groups such as sandeels. Its small mouth however restricts its feeding range. Spawning takes place along the south and southwest coasts, in March to June. Growth is rather slow, but females grow faster than males. Most of the males are sexually mature at 5, and females at 7. In Icelandic waters, the lemon sole can reach 14 years of age.

Lemon sole fishing grounds in 2007 (tonnes/nm2). All gear combined. Dark areas indicate hihghest catches.

Source: The Marine research Insittute

The witch flounder is a medium sized, rather long and thin flatfish, usually around 30 cm long, but the largest individual caught in Icelandic waters measured at 66 cm. It is found all around Iceland, but is much rarer in the colder waters north and east of the country. Mostly it occurs on mud or sand bottoms at depths between 50 to 300 m. It is found in European waters from Murmansk in the north to the Bay of Biscay in the south. It also inhabits seas around the Faroe Islands, in Greenlandic waters and from Labrador to Cape Cod in North America.

Witch flounder feeds primarily on polychaetes, but also to a lesser extent on other groups such as sandeels. Its small mouth however restricts its feeding range. Spawning takes place along the south and southwest coasts, in April to June. Growth is rather slow, but females grow faster than males. Most of the males are sexually mature at 5, and females at 7. In Icelandic waters, the lemon sole can reach 14 years of age. The distribution and biology of the witch flounder is remarkably similar as for lemon sole except that they prefer somewhat different bottom types.

Witch fishing grounds in 2007 (tonnes/nm2). All gear combined. Dark areas indicate hihghest catches.

Source: The Marine research Insittute

Dab is small compared to other flatfishes of commercial importance in Icelandic waters, usually between 20 and 35 cm in total length. The largest individual found in Icelandic waters was 48 cm, which is a world record. Growth is fast during the first years but slows after reaching sexual maturity at the age of 2 to 3 years for males and 3 to 4 years for females. Females grow faster and reach an greater age than males or up to 14 years. Dab probably spawns all around Iceland, earliest spawning starting from the middle of April off the southeast coast then spreading clockwise around the country. The last spawners are along the east coast where spawning probably starts around the middle of June. The diet of the dab is variable, it is an opportunistic feeder and can handle large food items. Various benthic invertebrates are common in the diet, as are sandeels and capelin. Discarded intestines from fishing boats are commonly found in dab stomachs.

The dab is exclusively a shallow water fish and is common on sand or mud bottoms from 0 to 40 m all around Iceland, and is rare below 120 m. It is more abundant in the warmer waters of the south and west coasts than along the north and east coasts. It presumably does not migrate long distances but generally seeks deeper waters in winter. Dab is only found in the eastern part of the North Atlantic, from the Barents Sea to the Bay of Biscay. In the North Sea, it is the most common fish species.

Dab fishing grounds in 2007 (tonnes/nm2). All gear combined. Dark areas indicate hihghest catches.

Source: The Marine research Insittute