Ecological aspects of larval drift in coregonids with long migration routes

Downstream migration (larval drift) of coregonids in the lower reaches of the Severnaya Sos??va River (the largest spawning tributary of the Lower Ob) has been analyzed from ecological aspects such as the long-term, seasonal, and daily dynamics and the spatial distribution, growth, and feeding of larvae in the current. Considerable changes in the abundance of coregonid generations have been revealed. It is shown that downstream larval migration over a long route has a number of features distinguishing it from that at spawning grounds. In particular, mass migration takes place after the ice drift, and its intensity is independent of changes in flow discharge. The drifting larvae display species-specific distribution in the current, and their density is the lowest in the surface water layer. In the course of migration, their linear body growth is accompanied by considerable depletion of endogenous food reserves and transition to active feeding.