Possible causes of variation of Champsocephalus gunnari vertical and horizontal distribution

C.gunnari form no aggregations during wintering period and inhabit places that are inaccessible for fishing. Conduction of census surveys during this period is pointless. In spring, during feeding period, they form aggregations near bottom thus being available for harvesting just at the beginning of this period (September). Data on stock assessment collected during accounting survey are good enough, however, this season is far from suitable for accounting surveys because of severe ice conditions. Fish feed intensively during feeding period in summer, performing vertical and horizontal migrations. It is not recommended to make stock assessment of fish yielded with bottom fishing gear, as in this case, fish staying in pelagic zone is missed. In autumn, pre-spawning fish migrate to spawning areas in near-bottom water layers where they are easy of access for fishing. C.gunnari, which do not spawn in the current year, continue feeding, but their feeding intensity considerably decreases and they gradually move to wintering areas. They can also be fished during such migrations.