Features of the omul (Coregonus autumnalis migratorius) distribution in different parts of Baikal Lake by acoustic data
Pelagic omul Coregonus autumnalis migratorius is the main commercial species of Baikal Lake. Its biomass was estimated for different bathymetric zones in different parts of the Lake on acoustic data obtained in the period from May 27 to June 9, 2003 by the echo-sounder Symrad EY-500 with towed antenna Split Beam (frequency 70 kHz, output power 610 W). Three bathymetric zones were examined: > 400 m; 200400 m;  400 m, 1326 % - above the depths 200400 m, and 411 % - in the shallow zone. The distribution was completely different in the area off the Selenga: only 10 % was in the deep-water zone, 18 % in the zone 200400 m, and 72 % - in the shallow zone. These features reflected complex patterns of redistribution the fish belonged to different populations and age groups of omul had migrating from wintering places to feeding grounds. To be more realistic, acoustic surveys in the deep zone must be conducted in detail in short terms. Usual May-June surveys limited by 400 m isobath underestimate considerably the stock of omul in Baikal Lake.