Density and biomass of Arctic charr Salvelinus alpinus (L.) complex (Salmoniformes, Salmonidae) from the two oligotrophic lakes at biotopes with different trophic levels

This investigation is aimed to estimate density and biomass of Arctic char Salvelinus alpinus (L.) from four points, different in trophic level and located in two oligotrophic lakes - Lama and Kapchuk, in Krasnoyarsk Territory and Taimyr, respectively. The samples were collected by gillnets from August 5 to September 3, 2019, near the mouths of two spawning rivers: the Nikita-Yuryah river flowing into Lake Kapchuk (69°48'N, 90°98'E) and the Bunisyak river flowing into Lake Lama (69°39'N, 91°59'E). One station was also chosen for each lake ~ 4 km away from the rivers’ mouths: the point (69°48'N, 91°88'E) on Lake Kapchuk and the point (69°41'N, 91°52'E) on Lake Lama. The sampling was conducted by placing single-walled gillnets with a mesh size of 20, 30 and 40 mm on the bottom, with 12 hours of fishing time. In total, there were 239 specimens of charr belonging to five morphotypes. Charr density in the four points was as follows, point 1-0.014 ind/m3, point 2-0.024 ind/m3, point 3-0.011 ind/m3, and point 4-0.027 ind/m3; charr biomass was: point 11.69 g/m3, point 2-4.72 g/m3, point 3-3.55 g/m3, and point 4-5.04 g/m3. In addition, the weight-length relationship was plotted jointly for all morphotypes from the four points. By means of pairwise comparisons of quantitative parameters (density and biomass), statistically significant differences in density and biomass were revealed between populations from the lake points and those from rivers’ mouths. The weight-length relationship is unique for each station that indicates stability of density and biomass values for the period of data collection. The relatively high charr density in the pre-mouth zones of spawning rivers demonstrates attractive effect of allochthonous organic introduced by the river flow. One of the morph, the “Goggle-eyed” charr (considered a deepwater species), is represented in the catches obtained from depths of 12-28 m, where the ratio of females at maturity stages III-IV reaches 30%. A comparative analysis of density and biomass carried out in different habitats allows assuming that there are background density and biomass of charr (and other species of fish) in both lakes, which is significantly lower than those in the high-trophic areas confined to the pre-mouth zones of spawning rivers. This hypothesis is also confirmed by the statistical analysis results which indicate non-random differences in density and biomass values. The fact that all morphotypes inhabit the same biotope may indicate wide feeding spectra of each morph, which makes it possible to effectively consume food resources in oligotrophic lakes. Therefore, it can be assumed that if Baranov’s principle of the dependence of fish abundance on food abundance is true for individual water bodies, it will also be true for zones/biotopes of one water body with different trophic levels. In this regard, the hypothesis that the gradient of density and biomass of charr population is equivalent to the gradient of trophic levels will be valid. The article contains 2 Figures, 2 Tables, 54 References. The author expresses gratitude to Osnov A.G., Lomonosov Moscow State University, for organizing the expedition and to Pavlov D.A. for consulting. The Author declares no conflict of interest.

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