Catalogue of Lakes in the Russian, Finnish and Norwegian Border Area = [Каталог озер в приграничном районе России, Финляндии и Норвегии] / Nikolay A. Kashulin, Vladimir A. Dauvalter, Sergey S. Sandimirov etc. - Apatity : Institute of the North Industrial Ecology Problems KSC RAS etc., 2008.

1.19.3. Hydrobiological studies Fig. 33. Distribution offish spe cies in Lake Kuetsjarvi. H yd rob iologica l ind ices The phytoplankton communities in Lake Kuetsjarvi, where diatoms predominate, have the highest biomass values (over 1700 mm3/m3). There are 54 species of phytoplankton in the lake (Sharov, 2004). According to earlier studies (Yakovlev et al., 1991; Noest et al., 1992), Lake Kuetsjarvi is the richest lake as regards the number of zooplankton species. The density of Cladocerae and Copepoda in the lake is the highest (up to 80000 specimens/m2) in the water bodies near the Pechenganikel smelter. The lake also has considerable species diversity of ground organisms. The number of zoobenthos species is over 20, ofwhich Chironomids are predominate (60-80%). Ichthyofauna. Studies on the fish community of Lake Kuetsjarvi were conducted in 1990-1992 and in 2002, 2005. Despite severe pollution by acidify ing compounds and heavy metals, the ichthyofauna of the lake is one of the richest ones of the lakes in the study area. The reason for this is that the wa ter body is connected to the River Pas- vik (the Barents Sea basin). According to the research data, the ichthyofauna of the lake consists of 9 species belonging to nine families of fish: trout ( Salmo trutta), whitefish ( C oregonu s lavaretus), vendace ( C oregonu s albula), grayling ( Thumallus thumallus), pike ( Esox lucius), perch ( Perea Buviatilis), burbot ( Lota lota), minnow (Phoxinusphoxinus), and nine-spine stickleback. The thornback ( Gasterosteus aculea- tus) obviously also inhabits the lake. Overall, whitefish and perch predominate in Lake Kuetsjarvi (Fig. 33). Pike, trout, grayling and burbot are occasionally caught. Two forms of whitefish inhabit the lake: sparsely rakered whitefish (up to 30 gill rakers) and densely rakered whitefish (with 30 - 40 gill rakers). The mean length and weight of the densely rakered whitefish are 12.2 cm and 28 g, respectively, with maximum values of 29.3 cm and 340 g.The bulk of the popula tion is represented by fish 8-12 cm long and weight of less than 50 g (Fig. 34) with an age of 0+ - 1+ (Fig 36a). A high proportion of the population of sparsely rakered whitefish consists of fish with a weight of 20-40 g and length of 10-16 cm. On the average they are slightly larger than the densely rakered whitefish (14.6 cm and 39 g), although maximum size of the fish is less (25.9 cm and weight 207 g) (Fig. 35). The age distribution of whitefish is dominated by 3-year-old fish; fish older than 6 years are caught only occasionally (Fig. 36b). Female fish ofboth forms slightly predominate over males (1:1.3). The most typical feature of the whitefish in this lake is early matu ration and spawning at an age of one year when they have attained a length of 9.5 cm and weight of 6 g. The mean size and weight of pike are 372 g and 32.4 cm, but individuals at the age of 6 have a weight of over 1 kg (1079 g) and length of 49.9 cm. The distribution of male and female fish is almost equal. The perch indices of Lake Kuetsjarvi do not exceed 164 g and 19.6 cm. The largest fish can be found near the lake channel and the River Pasvik but, overall, 44% of the fish have a weight of less than 100 g and length of 12-16 cm (Fig. 37). The age of the largest fish does not exceed 7 years. In the sex distribution there are twice as many females as males. 70 Catalogue o f Lakes in the Russian, Finnish and Norwegian Border Area