Demersal stocks

Most of the demersal fisheries are conducted over the Icelandic continental shelf. The main fishing grounds differ from one species to another on both large and small scale. This is due to several factors. The species might prefer different temperatures, generally more species are found in the warmer southern waters, and the number of commercially important species declines as the waters become colder. The species composition reflects changing temperatures in Icelandic waters. The monkfish, for example, used to be virtually absent from the waters west, north and east of Iceland. In recent years the ocean around Iceland has been warmer than usual and monkfish is now a common catch west of Iceland and is frequently found north of the country as well. A few species prefer the cold waters north of the country and are rarer in the south. These include Greenland halibut, northern shrimp and spotted catfish.

Harvested species also prefer different depth zones. A few species, mainly dab and lumpsucker (during the spawning period) are almost exclusively found in very shallow waters, at less than 50 m depth. Other species, especially juveniles, also occur there but are more common in deeper water. The most important fisheries are conducted at intermediate depths, below these shallow waters, down to a depth of about 200 m. This includes, for example, cod, haddock, saithe, plaice, Norway lobster and Atlantic catfish. Below that, down to 400 m depth, or sometimes deeper, important fisheries are conducted on redfish, Greenland halibut and northern shrimp.

The bottom type also has an impact on species composition. A few species, like cod or redfish, are generalist and can be found over many bottom types. Others are choosier in their bottom type preferences. Haddock and northern shrimp are mostly found over soft bottom as this is where they find food. Most flatfishes, with the notable exception of the lemon sole, also prefer soft bottom types. Examples of species that prefer hard bottom types are saithe, tusk and lemon sole.

The fourth factor influencing the distribution pattern of species is the availability of food; this is mainly controlled by ocean currents. The areas north-west and south east of Iceland are very productive due to the mixing of cold and warm currents. These are also the main feeding areas of the cod and the major fishing grounds for cod. Sites of abundant food supply also occur along the continental shelf breaks, where nutrient-rich deep sea currents are forced up by the topography of the bottom. This is where the major redfish fisheries are conducted in the warmer waters of the south and west and Greenland halibut fisheries in the north and east.

Most fish species aggregate in special areas during the spawning period. Furthermore, most species in high latitudes spawn during the spring, so that the juveniles are able to use the abundant supply of food during the spring bloom in both phytoplankton and zooplankton. The main spawning site for cod, haddock, and in fact many other species, is along the south-west coast. Except for the trawl fisheries, these are also the main fishing grounds and season for the demersal fleet. In 1970, for example, about 65% of the cod catch was taken from February to April off the south-west coast. Lately the landings have been spread more evenly over the year, as there have been measures to protect the cod during the spawning season. The markets also demand a more even supply of fish than these seasonal fisheries can provide.

Hörður Sævaldsson / Hreiðar Þór Valtýsson University of Akureyri