Sandimirov S.S. Assessment of the habitat conditions for the freshwater pearl mussel Margaritifera margaritifera (l.) In the headwaters of major rivers of Murmansk region. Conservation of freshwater pearl mussel Margaritifera margaritifera populations in Northern Europe. Proceedings of the International Workshop. Karelian Research Centre of RAS. 2010, p. 29-34.

CONSERVATION OF FRESHWATER PEARL MUSSEL MARGARITIFERA MARGARITIFERA POPULATIONS IN NORTHERN EUROPE The total density of S. salar parr in the spawning and nursery areas is high (Tab. 2), with the age class 1+ prevailing. These data are in conformity with previous results obtained for the Pana River (Kalyuzhin, 2003). The Kitsa River was found to have S. trutta spawning areas and juveniles in all riffle sites of the investigated section. The total density of trout parr in the spawning and nursery areas ranged within 18.4-48 individuals per 100 m2, which corresponds to the moderate level, with domination ofthe 1+ age class (Fig. 4, Tab. 3). Table 1. Size-at-age characteristics of salmon parr in the Chernaya River Age class Length АВ, cm Length АС, cm Weight, g 0+ (n=6) 3.3+0.09 3.13+0.07 0.33+0.02 1+ (n=12) 5.78+0.07 5.48+0.07 1.5+0.05 2+ (n=8) 8.3+0.04 7.85+0.06 4.2+0.07 Table 2. The density of salmon parr in the spawning and nursery areas of the Chernaya River in 2008 (ind./100 m2) (N = 26) Density in different age classes 0+ 1+ 2+ Total 31.5 63.0 42.0 136.5 Fig. 3. Age composition of Atlantic salmon parr in the surveyed sections of the Pana River in 2008 (N = 26) Fig. 4. Age composition of trout parr in the surveyed sections of the Kitsa River in 2008 Table 3. Size-at-age characteristics of trout parr in the Kitsa River (N = 7) Age class Length АВ, cm Weight, g 0+ (n=1) 1.2 5.5 1+ (n=5) 9.6+0.3 6.6 +0.6 2+ (n=1) 11.2 11.4 The surveys of the Tsaga River upper reaches revealed no sites potentially suitable for trout spawning and growth because of unfavorable riverbed characteristics, but presence of suitable trout spawning sites in the river lower reaches cannot be excluded. Benthic fauna and the European pearl mussel. The benthic community in the studied rivers comprises 12 groups (Oligohaeta, Hirudinea, Gastropoda, Bivalvia, Chironomidae, Ceratopogonidae, Thrihoptera, Coleoptera sp, Ditiscidae, Ephemeroptera, Odonata, Plecoptera) . All the invertebrate groups detected are included in the diet of salmonids (Shustov, 1983). Indicator-species of high water quality (Ephemeroptera, Plecoptera) were recorded in all rivers surveyed. Among-year variation of the water level in rivers is one of the key factors for finding mollusks. E.g., the exceptionally high water level in all studied rivers in 2008 made the survey results on potential mussel colonies unreliable. Further surveys of the Pana River in 2009 yielded more accurate results. The average length of the mussels (N = 30) found in the Pana River upstream of the confluence with the Chernaya River is 54.4 mm (ranging from 47 to 65 mm), average weight is 18 g (13—28 g), height - 28.8 mm (27- 32