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.

N.A. Kashulin, V. A. Shirokov, S. S. Sandimirov, L. L. Shchurov, P. M. Terent'ev, D. B. Denisov, S. A. Valkova ASSESSMENT OF THE HABITAT CONDITIONS FOR THE FRESHWATER PEARL MUSSEL MARGARITIFERA MARGARITIFERA (L.) 33 mm). The age of the mussels ranged from 12.7±0.25 to 17.7±0.25 years, averaging 17.9 ± 2.5 years. The corresponding parameters of mollusks from the Chernaya River were as follows (N = 31): length - 93.4 mm (56-101 mm), weight - 71 g (15-93 g), height - 44 mm (28-50 mm). The age of the smallest mussels was 15±0.25 years. Bigger specimens were older than 45 years. Although the density of mussels in the Pana River is low, the presence of relatively young individuals presumably testifies to ongoing reproduction of the M. margaritifera population in the upper reaches of the river. The low flow rate and riverbed characteristics in the upstream of the Tsaga River are unfavorable for pearl mussel habitation. DISCUSSION Some authors argue that water oxidation capacity of more than 15 mgO/l is a limiting factor for mussel populations (Zyuganov et al., 1993). Hydrochemically, the localities surveyed are favorable for the mollusk, especially the riffles, where salmonid juveniles were found, but at the very source of the rivers the flow rate is low, the bottom is silty, and host-fish are absent. It is common knowledge that, being natural adsorption agents, mosses play an important role in self­ purification of water ecosystems. The species composition of mosses in the region evidences good condition for M. margaritifera : oligotrophic, cold, transparent, fast-flowing waters. Analysis of the S. salar size-at-age structure in the Pana River shows relatively slow growth as compared with salmon from the other rivers. Besides, these values in 2008 were much lower than those previously recorded for the Varzuga River salmon. The reason for that could be negative hydrometeorological conditions during the year. A similar relationship was noted for trout parr in the Kitsa River. Surveys of the Tsaga River upper reaches did not reveal presence of pearl mussel populations either, but the river also lacked potential trout spawning and nursery areas. Low flow rate and riverbed characteristics in the upstream of the Tsaga River are unfavorable for pearl mussel habitation. Yet, one cannot exclude the mollusk may be present in the river lower reaches. It has to be mentioned that reliability of a study is strongly dependent on the water regime, as has been demonstrated by two-year studies. Thus, no definite conclusion can be drawn about the absence of the pearl mussel from the Kitsa River. Although the density of mussels in the Pana River in 2009 was very low, the presence of young individuals presumably testifies to ongoing reproduction of the M. margaritifera population in the upper reaches of the river. Special attention should be paid to the Pana River ecosystem as a significant salmon watercourse and to the Tsaga River, which will be exposed to serious impact after operation of the mining and processing enterprise begins. Its activities may jeopardize reproduction and spread of salmonid and mussel populations. Further control of the water quality and pollution, and study of the distribution of potential mussel habitats are needed. References Abramova I.I. & Volkova L.A. 1998. Identification guide to mosses o f Karelia. Moscow 390 p. (in Russian) Abramova A.L., Savich-Lyubitskaya L.I., Smirnova V.N. (1961). Identification guide to mosses o f the Arctic region o f the USSR. Leningrad 268 p. (in Russian) Algae Lichens and Bryophyta of the USSR/ 1978. Gorlenko M.V. (ed). Moscow: Mysl ’ 365 p. (in Russian) Amundsen P.-A., Kashulin N.A., Gjelland K.O., Sandimirov S.S., Jensen H., Shirikov V.A., Kudryavtseva L.B., Bohn T., Aspholm P.E. 2004. Brown trout in the Pasvik watercourse: population status and potentials and limitations for recruitment, production and management. NCFS, University o f Tromso, INEP 41 p. Bohlin T., Hamrin S., Heggberget T.G., Rasmussen G. & Saltveit S.J. (1989). Electrofishing theory and practice with special emphasis on salmonids. Hydrobiologia 173, 9-43 p. Hastie L.C., Boon P.J., Young M.R. 2000. Physical microhabitat requirements of freshwater pearl mussels, Margaritifera margaritifera (L.). Hydrobiologia 429, 59-71. Ignatov M.S. & Ignatova E.A. 2003. Moss flora of the central part of European Russia 1: Sphagnaceae - Hedwigiaceae , pp. 1-608. Moscow: KMK Scientific Press Ltd . (in Russian). Ignatov M.S. & Ignatova E.A. 2003. p Moss flora o f the central part of European Russia 2: Fontinalaceae - Amblystegiaceae, pp. 608-944 p. Moscow: KMK Scientific Press Ltd. (in Russian). 33