Survival of Early Burbot Larvae (Lota iota L., 1758) in the Ob Floodplain

The long-term data (2000-2017) on the abundance of burbot larvae (Lota iota L., 1758) during the downstream migration from the spawning areas in the spawning tributaries of the Ob River (the Voykar and Sob rivers) and in feeding areas in the floodplain system are analyzed. The average absolute abundance of feeding burbot larvae was 12.4 million specimens in the Voykar River and 7.3 million specimens in the Sob River. The average proportion of survived larvae which started exogenous feeding of the number of hatched larvae was 0.78 and 0.59%, respectively. The total abundance of feeding larvae is determined by the number of juveniles which migrated downstream from the spawning tributary: in the Voykar River, r(Sp) = 0.741, p = 0.006, in the Sob River, r(Sp) = 1.000, p < 0.001. The correlation between the survival of burbot larvae in the floodplain and environmental factors affecting the juveniles until their complete transition to exogenous feeding was found. For example, in the Voykar River the correlation between the survival rate and duration of flooding at the level of 7 m was r(Sp) = 0.732, p = 0.007; between the survival and average daily temperature for 14 days was r(Sp) = 0.921, p < 0.001; between the survival and the number of days of water warming above 8 degrees C, r(Sp) = 0.780, p = 0.003; in the Sob River the correlation between the survival and the average daily temperature for 14 days was r(Sp) = 0.900, p = 0.037. The linear regression equation describing the relationship between the larvae survival rate and the average daily water temperature for 14 days has the following form: y = 0.15x - 0.35, R-2 = 0.95. It is suggested that the main factor affecting the survival of feeding larvae is the availability of start feed (phytoplankton), the growth of which is determined by the levels of light and water temperature.