Catches, size and age composition of the spawning stock muksun Coregonus muksun in the Middle Ob (Tomsk region)

Abstract

Muksun Coregonus muksun is one of the most valuable whitefish species. It lives in large rivers of Siberia. This is a typical semi-anadromous species. There are presents data on the catches of muksun in the Middle Ob (on spawning grounds and migration routes to them), which generally reflects the number of spawning stock of this species rising to spawn. It is shown that in the middle of the 20th century the catches of muksun averaged 47 tons per year. In the early 1970s, there was a sharp short-term increase in its catches to an average of 215 tons per year, which may be caused by the start of intensive work on collecting whitefish caviar in the area of their spawning run for obtain fish stock for pasture aquaculture in the lakes of Western Siberia. Since the early 1980s, muksun catches have fallen catastrophically, and its fishing is currently prohibited. On the spawning grounds of the Middle Ob, specimens under the age of 16+ were noted. Until the end of the 1990s, the age and size composition of the Muksun spawning stock remained relatively stable. In recent years, there has been an increase of younger fish and, accordingly, a decrease in the average size of fish in the catches. At present (2017–2019), specimens with a fishing length from 392 to 523 mm (on average 457 mm) and a weight of 747 to 1915 g (on average 1233 g) have been noted in the catches of muksun.