Features of exploitation of high-number industrial chum salmon Oncorhynchus keta on the example of Lake Tunaicha (south-eastern Sakhalin): problems and proposed solutions

Abstract

In Lake Tunaicha mainly artificial reproduction of chum salmon is carried out. The escapement is at a high level — more than 1 million fish. Significant pre-settlement mortality of chum salmon has been regularly observed in the lake basin over the last three years (2019–2021). The scale of fish mortality was estimated based on the results of surveys of the lake, including those carried out with the help of UAVs. The data of fishing statistics, the filling of natural spawning grounds and the features of spawning chum salmon migration were analyzed. The sea surface temperature (SST) data was used. To assess the hydrochemical conditions in Lake Tunaicha during the period of mass entry of chum salmon spawners in 2019–2021, water samples were taken in the coastal area of Lake Tunaicha and in the estuarine sections of the rivers of its basin. The coastal marine fishery cannot keep up with the withdrawal of the commercial part of chum salmon return (no more than 10 %), and most of the fish migrate from the sea to the lake through the Krasnoarmeisky Strait. Before entering the rivers the chum salmon spends a long time in the lake (average of 11 days), and significant accumulations of chum salmon create a danger of fish mortality due to unfavorable hydrological conditions (low oxygen content, high water temperature), especially in shallow areas with an abundance of aquatic vegetation. It is necessary to organize the withdrawal of chum salmon brood stock surplus in the basin of Lake Tunaicha. Taking into account the nature protection status of the lake, this is only possible to implement in the Krasnoarmeisky Strait at the Okhotsk salmon fish farm fish accounting barrier. It is recommended to remove 50 % of the spawning chum salmon there from the beginning of its mass migration in the strait — from September 11.