The Dependence of the Duration of Downstream Migration of Burbot (Lota lota) Larvae on the Hepatosomatic Index of Spawners

Abstract

This study estimates the dependence of the duration of the downstream migration of burbot larvae in the Voikar River (the Lower Ob basin) on the relative condition factor of semianadromous spawners migrating upstream to the spawning tributary in autumn; the estimates are based on 20 years of observations (from 1999 to 2018). The observed (11 years) and calculated (9 years) values of the hepatosomatic index were used to estimate the relative condition factor of spawners. The values of the hepatosomatic index were calculated using the median quantile regression based on estimates of the maximum level of floodplain flooding and sum of daily average water temperatures during the open channel period in summer feeding areas. A strong, highly significant negative dependence of the duration of downstream migration of juveniles and of the number peaks of abundance larvae on the values of the hepatosomatic index of spawners has been revealed. It is assumed that there is a relationship between the relative condition factor of spawners and the timing of their upstream migration to spawning grounds. In turn, the upstream migration time determines the accessibility of river spawning areas for spawners, which then determines the timing of hatching of burbot larvae.