STATUS OF SIBERIAN WHITEFISH COREGONUS LAVARETUS PIDSCHIAN (GMELIN, 1788) IN THE SYSTEM THE TANJU RIVER - LAKE VARCHATO (THE VOIKAR RIVER BASIN)

The Voikar river is a spawning tributary of the lower Ob. Spawning grounds of Siberian whitefish are located both on the river Voikar and on the river Tanju (a tributary of the Voikar), which flows into lake Varchato. The Varchatovis canal flows out of lake Varchato and merges with the river Voikar. Studies have shown that in the system the Tanju river - lake Varchato live Siberian whitefish different from those of other Ural spawning tributaries of the Ob river and of the Ob itself by their age structure, presence of only re-maturing species with a high rate of growth and fecundity. It was found that after breeding on the spawning ground in the Tanju river some individuals of Siberian whitefish do not flow to the Ob river, but remain in system the Tanju river - Varchato lake. In two or three years it matures and goes back to spawn in the Tanju river, merging with the spawning stock which goes up the Ob river. There are no individuals that are constantly living in lake Varchato, as all juveniles, when still being larvae, flow down to the Ob river. That gives grounds for including Siberian whitefish of Varchato lake into the Ob population of semi-passing Siberian whitefish. The presence of re-maturing species in the system of the Tanju river - lake Varchato creates reproductive reserve of breeders that increase heterogeneity and population size. However, in the last decade as a result of total poaching of Siberian whitefish in lake Varchato during feeding and wintering its numbers declined sharply.