Size composition and distribution of Siberian sturgeon in the lower reaches of the Vilyui River in the early summer period of 2024

Abstract

The aim: assessment of the current biological status and distribution of Siberian sturgeon in the Vilyui River.

Material: data from a survey using bottom drift and fixed nets in June 2024.

Results: on the 470-kilometer section of the lower reaches of the Vilyui River, sturgeon were distributed unevenly: the average density was 197 specimens/km2, the highest density of 1307 specimens/km2 was reached in the middle part of the section, significantly thinning out to 7-28 specimens/km2 upstream and to 116 specimens/km2 downstream. In the area adjacent to the river mouth, sturgeon was not recorded in the catches due to a sharp rise in the flood level. In the sample series from the catch of drift bottom gillnets, the value of the commercial length of sturgeon (ac) varied from 36.0 to 60.0 cm, with an average of 47.6 cm. In the sample series of set gillnets, these values were 40.0-65.0 and 52.3 cm, respectively. The modal size class for Siberian sturgeon in the catch of 2024 was 41-50 cm (59% of the total catch). The average weight of an individual was 0.6 kg. There was not any individuals that had reached the size at which fishing is permitted (> 62 cm) in drift bottom gillnets; while the proportion of commercial individuals was 7% in set gillnets. Sexually mature individuals were not noted.

Practical value: results will be used to assess the size and weight composition of part of the Siberian sturgeon population feeding in the middle reaches of the Lena River.