Koroleva I.M. The status of whitefish population from Chuna Lake in the Lapland Biosphere Reserve Russia. International Journal of Environmental Research. 2008, V.2, №2, p. 111-124.

The status o f whitefish population pollution, with the water composition characterized by seasonal variations in the dynamics of pollution supply. Inwinter, there is a great amount ofacidifying agents and heavy metals accumulated in the snow cover during 7-8 winter months. In spring, due to intensive snowmelting, these pollutants drain into the lake. Seasonal pH-decrease and heavy metals concentrations fluctuations are due to a considerable input of acid-forming agents in this period (Table 2). Despite the relatively stable Cu andNi concentrations in Lake Chuna (Table 2), the seasonal dynamics data on the weighted mean o f these elements concentration in Lake Gornoe (fromwhere the Chuna originates to flowthen into Lake Chuna) demonstrate dramatic increase in these elements concentration in the lake water in spring flood (Fig. 2). The bottom sediments have been analyzed to show a considerable increase in the major (Cu, Ni) pollutants concentration in sediments, from bottom to top. The metals concentration in the upper layers o f sediments which were produced by the “industrial” period, exceed twice, and even more, tha t o f the deeper layers which are o f the background level. The values of contamination factor were the maximum ones in the eastern (the widest) part of the lake, which was earlier referred to as a feeding area (Table 3). It is likely connected with the fact that this area is characterized by less intensive flowage. High levels of bioaccumulation of Cu and Ni in whitefish organisms are likely to be due to the fact that whitefish inhabits the feeding area for a greater part of the year and, according to its feeding peculiarities, lives near the bottom. The studies have revealed that the eastern and widest part of the lake is less running, shallow and generally the most favorable for whitefish feeding. The westernmost part of the lake, where the Chuna River flows into it, is deep and is inhabited bymature fish of elder age-groups participating in or non­ spawning in the year. This area was defined as a spawning zone.Lake Chuna is inhabited by sparsely rakered whitefish, with the number of gill rakers from 18 to 30. The whitefish is of small size. The mean weight is 258 g, the mean length AC is 28.5 cm. The maximum weight and lengthAC are 916 g and 41.2 cm, respectively. Juvenile fish made up 2.1% of the catch. These were fish at the age of 1+ and 2+, whose mean weight and length AC are 39 g and 14.2-18.8 c, respectively. All the juvenile individuals were caught in the eastern shallower part of the lake that is a feeding area. The whitefish of younger age groups, 1+ - 3+, were caught in a practically equal proportion. Over a 50-year period, the age structure of whitefish population of Lake Chuna has undergone considerable changes, i.e. the number of the age groups has decreased. The mean age of the population has decreased due to lifetime reduction and increase of the share of younger age groups. According to the early 1960s studies, whitefish population accounted for 13-16 age- groups and the most numerous was fish at the age 6+ (V ladim irskaya, 1951; Reshetnikov, 1996). The maximum age of the current whitefish population is 10+ and the most numerous is fish at the age 5+. Moreover, there were found only single individuals at the age of 8 years (Fig. 3). At present, the number of fish over 5+ accounts for 38.8%, while in the 1960s, this index was much higher (64.5%) (Table 4). Thus, young fish dominated in the catch. The mean size characteristics of whitefish have not significantly changed over the last decades, accounting for 28.6 cm and 260 g against 29.0 cm and 275 g, in the 1960s (Reshetnikov, 1962). Though, at present, the size of whitefish has decreased in old age groups (Table 5). It necessary to note that whitefish of the same size is of a lower weight compared to the earlier data, which can also be indicative of changes’ having taken place, which in turn can be explained by lesser fish fatness (Fig. 4). The comparison of reproduction features of whitefish in the lake has also revealed serious changes. That the whitefish inhabiting the northern water bodies misses spawning is a well known fact, which is due to a short vegetation period in water bodies and to the age and sexual composition, and the feeding conditions (Reshetnikov, 1967, 1980). The current whitefish population participates in spawning at the age of 4+. The minimum size of the fish spawning for the first time, is 23.2 cm/ 142g and 28.0 cm/225 g for male and female fish, respectively. The earlier data (Reshetnikov, 1965) show that at the age of 4+ it was only single male whitefish that became matured, and that the minimum size ofthe fish spawning for the first time, was 28.5 cm /250 g and 29.2 cm/300 g for male and female, respectively. The early mass maturation took place at older age when fish was of a larger size, with weight difference being greater against size ones (Fig. 5). This fact is indicative of rejuvenation ofthe matured part of the population. 114