TITOV O.V., LEPESEVICH YU. M., PEDCHENKO A.P., PLOTITSYNA N.F., NOVIKOV M.A., ZHILIN A.YU.
Polar Research Institute of Marine Fisheries and Oceanography, Russia

The Barents Sea ecosystem is situated on the borderline between the warm Atlantic and the cold Arctic waters, i.e. in the area where two oceanic systems interact.

This determines both the climate and biological features of this ecosystem. Living resources of the Barents Sea usually inhabit certain water types. The main fish species, cod and capelin, occur predominantly in the boreal and the Arctic oceanic systems.

The Barents Sea is the most productive water reservoir in northern Russia. It is inhabited by 207 fish species of 69 families (Andriyashev, Chernova, 1994).

Of all Barents Sea fishes, ca. 20 are commercial ones. The main target species are cod, saithe, redfishes, flounders, catfishes, capelin, polar cod, shrimp, Atlanto-Scandian herring and blue whiting. Red king crab introduced in the Barents Sea also started to play an important role in fishery in the recent years as its stock has notably grown. The Barents Sea is the eastern and northern margin of the distribution area for many marine species. As a result, drastic variations in environmental conditions and the following yearclass strength fluctuations are very likely to occur. Appearance of an abundant yearclass or a sequence of strong cohorts causes fundamental changes in length and age composition of populations and determines long-term trends in the stock development and fishery.

Modern status of the main commercial stocks offish and invertebrates is characterised by the following. Capelin, S.marinus and S.mentella are in a state of depression, their abundance and biomass being close to the historical minimum. Fishery on these species is banned and they are taken only as bycatch. Despite the positive trend, the Greenland halibut stock is well below the long term mean and the ban on this fishery is still in force. Abundance and biomass of saithe and northern shrimp are close to the long term mean. Overfishing and incompliance with scientific advice on catches and fishery caused downward trends in the abundance of cod and red king crab. Haddock and polar cod stocks are in a good condition. Due to a number of strong yearclasses the biomass of the commercial and the spawning stocks considerably exceed the long term mean. In 2005, mean catch of marine resources in the Barents Sea and the adjacent waters was estimated at ca. 400 000 tonnes. In case of a continued positive anomaly in the Barents Sea, Russian catch of marine species will remain at the same level provided that PINRO recommendations are observed and the current stock management principles are followed.

The Barents Sea is characterised by a wide range of year-to-year variations in the water and air parameters. The climate system of this area comprises three main components, i.e. atmosphere, hydrosphere and cryosphere. Interannual variability in these components is estimated using long-term observations of air temperature, water temperature and ice coverage of the Barents Sea (annual mean). Over the last 50 years, different areas of the Barents Sea showed similar trends of temperature variations (Boitsov, 2006).

The investigations have indicated an upward trend in air temperature in the last decade. In the western and northern Barents Sea, long term maxima for the entire study period were observed. Similar processes occur in the hydrosphere. Investigations on the centennial Kola Section are indicative of anomalously high temperatures in the Barents Sea in 2000-2005. General warming in the ocean-atmosphere system resulted in the ice coverage reduction in the Barents Sea. Similar situations were also observed in the previous years. This is proved by year-to-year variations in the climate index over the period from 1990.

A period of similar warming in the Arctic was observed in the 1930-50s. However, the duration of the current warm period is less than that of the previous one, and climate indices for the beginning of the 21th century are lower than the extreme indices of the 1930-50s. Long-term forecasts made in PFMRO suggest that temperatures in the Barents Sea are likely to drop to the long term mean in the coming decade.

The main sources of the Barents Sea pollution are the North Atlantic current, long-distance atmospheric transport, navigation and industrial activity in the coastal areas. The monitoring is presently focused on aliphatic (oil) hydrocarbons (OH), polycyclic aromatic hydrocarbons (PAH), organochlorine pesticides (OCP), polychlorinated biphenyls (PCB) and heavy metals (Me). Investigations conducted in the last five years suggest low concentration of pollutants in the Barents Sea commercial fishes and in their environment.

Concentrations of pollutants usually do not exceed national standards or the global background level. For example, concentrations of oil hydrocarbons in the Barents Sea water vary from 1 to 50 mkg/1, those of PAHs lie around the global background level of 20 ng/1 (Cripps, 1995), while those of PCB and OCP are well below 10 ng/1 (Reference list of fisheries..., 1999). The content of oil hydrocarbons in bottom sediments ranges from 0.1 to 70 mkg/g dry weight, not exceeding the background level typical of the surface layer of bottom sediments on the West Arctic shelf (Gurevich, 2002). Concentrations of PAHs in the bottom sediments off Spitsbergen which is rich in coal deposits are considerably higher than in other marine areas.

The content of OCPs in the bottom sediments of the Barents Sea ranges from 0.5 to 3 ng/g dry weight, the content of PCBs does not exceed the technogenic background level of 5 ng/g dry weight (Klassifisering av milj0kvalitet,.., 1997). Concentrations of heavy metals are generally also close to the background level. Spatial distribution of persistent organic pollutants and heavy metals agrees well with their granulometric composition and concentration of organic carbon.

Prevalent in organs and tissues of the Barents Sea commercial fishes are oil hydrocarbons of biogenic origin. Mean content of «-paraffins in muscle of cod, haddock and saithe does not exceed 4 mkg/kg wet weight, while in muscle of long rough dab and redfishes it does not exceed 9 mkg/kg wet weight. Summarised content of PAHs in muscle of cod, haddock, saithe and long rough dab does not exceed 10 ng/g wet weight, in muscle of redfishes it does not exceed 50 ng/g wet weight. Summarised concentrations of PCBs in muscle of lean fish were not more than 3 ng/g wet weight, while those found in muscle of Greenland halibut and lumpsucker containing over 10% of fat reached 8 ng/g wet weight. The prevailing heavy metals found in fish muscle were iron and zinc. The content of such toxic microelements as lead, cadmium and mercury lies at the background level.

Concentrations of pollutants in fish liver are generally higher than in muscle as liver is a storage organ which accumulates the greatest amount of pollutants. Nonetheless, comparison of the results with published data on the commercial marine stocks is indicative of pollutant content in muscle and liver of the Barents Sea fish not exceeding the sanitary standards for marine fishes and seafood (Hygienic standards,... 2002).

Development of oil and gas fields can have a considerable impact on the marine environment and biological resources of the Barents Sea. Pollutants are being brought and spread in the Barents Sea mainly with the North Atlantic current.

This is the cause of concern related to eventual discharge of pollutants under the development of the Snohvit and Goliat fields in the Norwegian sector of the sea. To estimate vulnerability of the Barents Sea ecosystem to anthropogenic pollution, PINRO compiled integrated maps (fig. 4) which show the main ecosystem parameters, including distribution and fishery of marine species (Novikov, Plotitsyna, 2003). Higher concentrations of pollutants in the Barents Sea water are found at the convergence of different water masses (frontal zones) and in the areas of quasi-stationary gyres (Israel, Tsyban, 1989). An eventual increase in the anthropogenic pressure on the Barents Sea related to water pollution will primarily affect the most vulnerable marine areas.

References
Andriyashev A.P. and Chernova, N. V. Annotated list of fish-shaped and fish species of the Arctic seas and adjacent waters. //Voprosy Ihtiologii. 1994. V.34, 4: 435-456 (in Russian).
Boitsov V.D. Variability of water temperature in the Barents Sea and its Lorecasting. 2006 - Murmansk? PINRO (in press).
Cripps G.S. Baseline level of hydrocarbons in sea water of the Southern ocean. Natural variability and regional patterns. //Mar.Poll.Bull. 1995. V.30, 2:133-145.
Gurevich, V.I. Modern sedimentogenesis and geoecology of Eurasian West Arctic shelf. Moscow: Nauchny Mir Press, 2002. 135 pp. (in Russian).
Hygienic standards of security and nutritional value of food products (SanPiN 2.3.2. 1078-01). Moscow: Minzdrav of the Russian Federation, 2002. 164 pp. (in Russian).
Israel, Yu.A. and Tsyban, A.V. Anthropogenic ecology of the ocean. Leningrad: Gidrometeoizdat Press, 1989. 528 pp. (in Russian).
Klassifisering av milJ0kvalitet I fjorder og kystfarvann. Veiledning. J.Molva?r, IKnutzen, J.Magnusson, B.Rygg, J.Skei, J.Serensen. In: SFT Veiledning, 97:03. 1997. 36 pp. (in Norwegian).
Novikov, M.A. and Plotitsyna, N.F. Ecological and fisheries atlas of the Barents Sea (digital resource). 2003.- Murmansk: PINRO Press. 1 CD ROM.
Reference list of fisheries standards: maximum allowable concentrations and estimated safe levels of pollutants in fisheries waters. 1999.- Moscow VNIRO Press. 304 p. (in Russian).

OIL AND GAS OF ARCTIC SHELF 2006 (PROCEEDINGS OF INTERNATIONAL CONFERENCE)