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In recent decades, non-indigenous species which may be considered both “introduced” and “invasive” have appeared in the Barents Sea. Currently, 15 of them have been identified. These organisms entered the Barents Sea either in a natural manner — through the expansion of habitat due to global warming — or as a result of human activities, related to the intentional or accidental introduction of non-indigenous species.
At present, studies related to the invasive species are mainly focused on two species of crabs: Red king crab (Paralithodes camtschaticus) and Snow crab (Chionoecetes opilio). Fisheries are conducted for these crab species; both are considered to be of economic importance. Scientific information regarding other invasive species is fragmentary and requires further research.
Annotated list of species introduced into the Barents Sea
- Codium fragile ssp fragile (a seaweed). The taxonomic resolution of the complex is uncertain. The subspecies regarded as the most invasive, C. fragile ssp tomentosoides, currently has a more southerly distribution. It is regarded rather unlikely that C. fragile-species will have serious impacts on the Barents Sea Ecosystem
- Bonnemaisonia hamifera (a marine alga) is found in the littoral and in littoral ponds along the coast. There is a limited knowledge on effects and spread. It is regarded rather unlikely that B. Hamifera will have serious impacts on the Barents Sea Ecosystem
- Caprella mutica (Japanese skeleton shrimp) was first observed in W. Norway in 1999. Today observed along the coast around Tromsø. There is little knowledge on effects on ecosystem or indigenous species
- Heterosiphonia japonica (red seaweed) is currently not found north of Trondheim. Has grown and spread fairly aggressively south and north of the place originally observed close to Bergen
- Molgula manhattensis (marine invertebrate). This sea-squirt is currently found in southern Norway, not in the Barents Sea proper. Hard-bottom species
- Balanus improvisus This barnacle has been established in Norwegian waters since first half of 20th century. May compete with indigenous barnacles for space and food. Limited knowledge on other effects and current northern range
Red king crab (Paralithodes camtschaticus)
Red King crab was introduced deliberately to the Barents Sea in the 1960s by Soviet scientists, and the stock has increased heavily in abundance as well as in distribution. The crab is now common in coastal areas from Cape Kanin in the east to Northern Troms in the west. It is a highly valuable product on the market. The red king crab fishery in the Barents Sea started as an experimental fishery in 1994 with a quota of 11,000 crabs in both the Norwegian and Russian zones. This quota increased during the 1990s to 100,000 in 2001. In 2002, the Norwegian king crab fishery became a commercial fishery with vessel-quotas, while the Russians introduced a licensed commercial fishery in 2004.
Despite agreements during 2005-2007 to establish common principles of management of a new biological resource, both Norway and Russia managed fisheries for the red king crab stock separately within their respective economical zone, and agreed to inform each other about the national measures taken. In Norway, the main research goals have been to reveal the effects of red king crab on the ecosystem and to prevent its further distribution in Norwegian waters. In Russia, however, the main focus is on rational harvesting of the stock. In Norway, the crab fishery is subjected to two different regimes. In a limited commercial area east of 26o East, the crab stock is harvested as a sustainable commercial species; while outside this area there is a non regulated free fishery aiming to prevent further spreading of the crab. In the Russian zone, fishery regulations are still based on principles agreed upon with the Norway. Thus, fisheries for the red king crab stock are subjected to three different management principles: 1) in Russian waters they are based on elements of the precautionary approach; 2) in open Norwegian waters and to the west of North Cape, there is an open fishery to prevent spreading; and 3) in the fjords of eastern Finnmark the fishery is aimed to maintain a low stock level.
Impact of red king crab on the Barents Sea ecosystem
The impact of red king crab on Barents Sea benthic fauna was a significant theme in two three-year Joint Russian-Norwegian research programs on this species during 2002-2004 and 2005-2007. This species was studied both in terms of its population expansion and its impact on benthic communities. Central topics were the effects of red king crab feeding activity on the benthos, and the interspecies relationships between the crab and other commercial species with emphasis on red king crab both as both a predator and as a competitor for available food resources.
Motovsky Bay in the southern Barents Sea was the main area for these studies. This area was chosen because red king crab has been abundant there since its introduction to the Barents Sea. In addition, published results from studies conducted — during 1931-1932 and 1996-2003 — on the benthos in this Bay were available. The king crab has inhabited this area for more than four decades, and appears to have successfully adapted to its new environment. The benthic community in this area is dominated by the sedentary polychaete Maldane sarsi. Results indicate that red king crab has not had a significant impact on either indices of species abundance or species diversity for the benthic community in the deep-water of the Bay. The local variations in total biomass and the structure of the community recorded in the open part of the bay was probably due to fishing activities which was mainly carried out in the open north-eastern part of the Bay. It is believed that observed changes within benthic communities in this area were more likely caused by the fishing activities than by an abundant king crab stock feeding in the area. The influence of the red king crab on the Iceland scallop stocks was studied by analyzing the stomach content of crabs in non-harvested parts of the scallop beds, and on scallop beds that were harvested. These investigations showed that crabs foraging on beds that were harvested consumed significantly more scallops than in areas where there were no scallop fishery going on. The observation of scallop fragments in the crab stomachs may indicate that, in harvested scallop beds the crabs primarily consume wastes of scallop from the fishery and specimens damaged by the dredge. In beds with no fishing the crabs feed exclusively on young scallops.
In the Varangerfjord, close to the Russian-Norwegian border, detailed studies of the benthic community had been done at two locations in 1994, just prior to the invasion of the red king crab. In 2008 the sites were revisited and large changes in the benthic communities were found. In one of the locations, the most striking observations were a total absence of the mud sea star (Ctenodiscus crispatus) and a significant reduction of brittle stars (Ophiuroidea). In 1994 Ctenodiscus was present in a density of 10-15 ind./m2 here. In addition, several species of bristle worms and bivalves were reduced or absent. In the other location, it was observed a similar reduction or absence of large specimen of biologically important taxa. For example, no brittle stars of any species were observed in 2008, and very few specimens of the sea urchin (Strongylocentrotus droebachiensis) — which were common in 1994 — were observed in 2008. The bivalves Mya truncata and Macoma calcarea were highly reduced, and only some few larger specimens were found. It also appeared that smaller bivalve species was reduced or absent. Among the bristle worms, Harmothoe imbricata, which were abundant at the shallowest station (10m depth) in 1994, seemed to be totally absent in 2008. The same holds for Nothria conchylega, which were common at the two deepest stations in 1994 and not recorded in 2008. The authors of the study conclude that the observed changes are likely to be caused by feeding activities from the king crab (Oug and Sundet, 2008).
Feeding of the crab on fish eggs during spring has been documented. However, the long-term observations showed that, on the average, in spring, the frequency of occurrence of fish eggs in crab stomachs was less than 6% and the weight portion in the crab diet less than 2%. The highest frequency of occurrence of fish eggs (mainly capelin eggs) in crab stomachs were registered in 2001 (19.4%). Preliminary estimations indicate that in this particular year about 37 tonnes of capelin eggs were eaten by red king crabs in Western Murman waters. In the Russian Economic Zone, the capelin spawning stock accounts for the one third of the total spawning stock and was estimated to be 99.5 billion individuals in 2001. The weight of anegg clutch from one female capelin is on the average 8 gram. Thus, the total amount of eggs spawned by the capelin stock in 2001 in Russian waters is estimated to 130 thousand tonnes. The simple calculations therefore show that, in 2001, the red king crab ate about 0.03% of the weight of all capelin eggs spawned. It is therefore reasonable to believe that the king crab feeding on eggs does not influence the capelin spawning stock significantly.
Long-term studies indicate that the main food items for red king crabs in the Barents Sea — echinoderms, molluscs, and worms — are also major prey species for the haddock. Therefore, any food competition between the red king crab and haddock should result in lower frequency of occurrence in haddock stomachs. A comparative analysis of haddock stomach content during a period (1971-1977) of low red king crab abundance with a period of increased red king crab abundance (1995-2002) was conducted; this analysis did not indicate any direct food competition between these two species in the Russian part of the Barents Sea.
Snow crab (Chionoecetes opilio)
After snow crabs were first observed on Goose Bank in 1996, the number of reports on snow crab by-catches in bottom-trawl fisheries has gradually increased (Pavlov, 2002). Since 2003, the snow crab has been observed in stomachs of cod, haddock, catfish, and thorny skates. Thus, snow crabs have became a new food item for bottom fish in the Barents Sea. In 2005, the first snow crab was captured during the ecosystem survey. During 2005-2008, both the number of trawl stations where this species occurred and the number of individuals per station increased. During that period, the crab occurred in bottom trawl catches in most of the eastern Barents Sea — concentrated mainly in areas adjacent to Goose Bank and the southern extremity of Novaya Zemlya.
In 2007-2008, directed trawl surveys for snow crab were initiated; Goose Bank and adjacent areas in the eastern Barents Sea were surveyed. During these surveys, the highest snow crab abundance was 95 specimens per haul/hour. Males were predominated (84%) in the catch, and greatest density of crabs (145-320 ind./km2) occurred south of Goose Bank.
Survey results indicate that the snow crab has adapted to the Barents Sea; it is assumed that its abundance will increase in the eastern Barents Sea in the near future. Due to this, it is expedient to monitor both distribution and abundance of this species regularly, and to evaluate its impact on the ecosystem.