Cooperation in stock management
JRNFC). At the first stage of the work (1993-2001), the main purpose was to prepare a common strategy in the management of the stock which was considered to be a joined stock. It was proposed that by dividing the commercial stock into self-reproducing subpopulations, it was reasonable to have a separate management, i.e. to establish a TAC for each stock unit. Based on a long-term research, the JRNFC approved a proposed management regime and measures for the king crab management in 2000 and 2001 respectively.
The main principles of the strategy were the rule of three “S” (Sex, Size, Season), i.e. only males with a minimum legal size could be harvested at a certain level of exploitation using only traps in autumn-winter.
However, despite the reached agreements to establish common principles of management of a new biological resource, in 2005-2007, both parties agreed to manage the crab stock separately within their respective economical zone, and only to inform each other about the national measures taken. In Norway, the main research goals have been on revealing the effects of the red king crab on the ecosystem and prevention of its further distribution in the Norwegian waters. In Russia, however, the main focus is on a rational harvest of the stock. In Norway, the crab fishery is subjected to two different regimes. In a limited commercial area east of 26 o E 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 the principles agreed upon with the Norwegian party. Thus, the new stock of the red king crab is subjected to three different management principles: in the Russian waters they are based on elements of the precautionary approach; in the open Norwegian waters and to the west of the North Cape, there is an open fishery to prevent spreading, and in the fjords of eastern Finnmark, the fishery aimed to sustaining a low level of the stock.
The effect of red king crab on the Barents Sea ecosystem
The study of impacts of the red king crab and the Barents Sea fauna were significant themes in two three-year Joint Russian-Norwegian research programs on this species during 2002-2004 and 2005-2007. The consequences of the red king crab were studied both at a crab population and a benthic community levels. Main subjects were effects of the crabs feeding activity on benthos and the relations between the crab and other commercial species with emphasis on the crab being a predator and a competitor for prey organisms.
The Motovsky Bay in the southern Barents Sea was the main area for these studies. This area was chosen since it was the area where the crab has been abundant since the introduction to the Barents Sea. In addition, there are several published results from earlier investigations on the benthos in this bay, during 1931-1932 and 1996 - 2003. The king crab has inhabited these areas for more than four decades and is probably most adapted to its new environment here. The benthos community in this area is dominated by the sedentary polychaete Maldane sarsi.
Investigations showed that the red king crab has not had any significant impact on the indices of abundance and the diversity of the benthic community in the deep-water part 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 northeastern part of the bay.
In conclusion, it seems that the observed changes in benthic communities in this area were more likely induced 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 at all in 2008 and very few specimens of the sea urchin Strongylocentrotus droebachiensis were found, which were common in 1994. 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 was abundant at the shallowest station (10 m 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, E. and Sundet, J.H., 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 t of capelin eggs were eaten by crabs in the 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 99.5 billion individuals in 2001. The weight of an egg 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 tons.
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 significantly on the spawning stock of capelin.
Long term studies have shown that the main food items of the crab (echinoderms, molluscs, worms) in the Barents Sea are also major prey species for the haddock. Therefore, any food competition between the king crab and haddock should result in lower frequency of occurrence in haddock stomachs. A comparative analysis of haddock stomach content in the period of low abundance of the red king crab (1971-1977) and when its abundance increased (1995-2002) was made. The analysis made did not reveal indications of any food competition between these two species in the Russian part of the Barents Sea.