Assessment of the complex effects of fisheries and hydrological conditions in Kamchatsky Gulf on formation of Pacific salmon spawning stocks in Kamchatka River

Abstract

The paper represents results of longterm analysis of the state of the Pacific salmon stocks in Kamchatka River. It is admitted, that high-level effects of fisheries resulted in degradation of the spawning stock (stock abundance) of major local salmon stock units in the basin of Kamchatka River. Commercial importance and previous reproduction potential of all Pacific salmon species has been lost in the mediate and upper parts of the river. This situation was especially noticable in 2018–2020.In view of the trend in the dynamics of salmon stocks in the Kamchatka scientists of KamchatNIRO suggested additional measures of fishery regulation in the Kamchatsky Gulf and Kamchatka River basin. A target strategy of management of fishing Pacific salmon in Kamchatka River was developed as a result, including a complex of limitations to start fishing (catches), a system of stop-fishing days and periods of full stop fishing to provide escapement for spawning.Moreover, regular annual biological monitoring of Pacific salmon of Kamchatka River, provided by KamchatNIRO, was noticeably strengthened with additional hydroacoustic counting and control fishing at the fishery plot № 832. Hydrological-hydroacoustic surveys in Kamchatka Gulf began in 2018 also were to improve the regional scientific monitoring.Results of the surveys 2019–2021 allowed to evaluate current effects of hydrological regime and fishing in Kamchatka Gulf on formation of salmon spawning stocks in Kamchatka River. It has been found, that the changes of the morphodynamics of the Kamchatka River mouth in 2021 resulted in wider area of freshwater effects in Kamchatka Gulf. That was a trigger of redistribution of prespawning salmon aggregations on their migration routs to the river mouth, what eased press of fishing in the area of plots of marine fixed gill nets. In this way the spawning escapement of Pacific salmon into the basin of Kamchatka River this year increased.