In the Barents Sea around 100 fish species occurs regularly in survey trawl catches. The total biomass and abundance is dominated by few species; for instance, the ten most abundant fish species constituted over 90% of the total abundance of all species caught in bottom trawls on the ecosystem survey in August-September 2004-2008 (Figure 2.4.12).
More than 200 species from 70 families have been registered in the Barents Sea. The most important families are: eelpouts (Zoarcidae), codfishes (Gadidae), sculpins (Cottidae), snailfishes (Liparidae), skates (Rajidae), flatfishes (Pleuronectidae) and rocklings, lings and tusk (Lotidae). These families account for over 80 % of the species regularly occurring in the Barents Sea.
The different fish species are not evenly distributed in the Barents Sea, but have highest abundance in the areas where the environmental conditions suit their preferences. The different water masses, i.e. coastal water, Atlantic water, Arctic water and the frontal zones between these water masses, together with bottom type and depth, are important factors determining the distribution and abundance of the fish species. For pelagic species the distribution and abundance of zooplankton is also very important. Species with the same environmental preferences will co-occur in limited geographical areas and form fish assemblages, with distinctive species compositions .Figure 2.4.13 shows how different demersal fish assemblages were distributed in the Barents Sea in August-September 2007.
There is a distinct species grouping north of the Polar Front in Arctic water, two frontal groups (one deep and one shallow) and one grouping in the southwest and along the shelf associated with warmer Atlantic water. There are also several coastal groups, along Spitsbergen, the Norwegian coast, the Murman coast and the coast of Novaya Zemlya. Each of these groups are characterised by their species composition and by the relative abundances of the species present.
Andriyashev and Chernova (1995) classified fish 166 species recorded in the Barents Sea into seven zoogeographical groups (see Table 2.4.1 for definitions). Out of these107 are regularly occurring (Figure 2.4.14).
All of the species classified as Arcto-boreal and Mainly boreal are regularly occurring. The Arctic species have their southern distribution border in the Barents Sea north of the polar front. Some of the Arctic species are deep water species belonging to the polar basin, and 80 % of the Arctic species recorded in the Barents Sea are regularly occurring. The species classified as Boreal and South Boreal have their northern distribution border in the Barents Sea, and 50 % of them are regularly occurring. Less than 10% of the Widely Distributed species are regularly occurring, and can be considered as vagrants. Due to the recent increase in temperature in the Barents Sea, the increased inflow of Atlantic water and the range expansion of many fish species found in southern areas, new recordings of Boreal, South Boreal and Widely Distributed fish species are to be expected in the Barents Sea.
The cluster analysis was done using the software PRIMER, applying Bray Curtis similarity and a Cut off level for low contributions of 90.00%. The abundance data (number of individuals per haul) was standardised into numbers per 3 nautical miles towed (i.e. comparable with 1 hour trawling) and log transformed. The three most abundant species (cod, haddock and long rough dab) was excluded from the analysis. These species are abundant and ubiquitous in the entire survey area and analyses incorporating these species showed a pattern reflecting the abundance variation of these species while not revealing any information on the overall species composition and assemblage structure and distribution.