Conservation measures for Wels catfish (Silurus glanis Linnaeus, 1758) stocks in the Volga River delta and the Northern Caspian Sea

The study demonstrates the ongoing deterioration of fish habitats in the Northern Caspian Sea and the Volga River delta. An analysis was conducted on the factors influencing the conservation of Wels catfish stocks in these regions. In recent years, the reproduction of catfish in the Volga River delta has occurred under an unstable hydrological regime, characterized by habitat contraction and the degradation of spawning and foraging conditions, particularly for younger age groups. It was established that catfish yields significantly depend on abiotic factors, such as fluctuations in the Caspian Sea level, Volga River flood volumes, and the timing of spring floods and water warming. Furthermore, a decline in the abundance and condition factor of the catfish's food chain components has negatively impacted its nutritional status and the growth rate of juveniles. An analysis revealed a decrease in the mean length and weight of individuals aged 3–5 years. The study also evaluates Russian Federation legislation regarding the conservation of aquatic biological resources and fishery regulations as applied to Wels catfish in the Volga River Delta and the Northern Caspian Sea. Given the predicted decline in catfish stocks within the Southern Fisheries District of the Volga-Caspian basin, additional conservation measures are proposed: increasing spring water discharge; expanding the Volga pre-estuary prohibited zone while establishing a differentiated fishing regime for major seasons; raising the minimum commercial size to at least 70 cm to ensure 100% maturation of first-time spawners; reducing the percentage of undersized bycatch in traps and seines; and intensifying anti-poaching efforts at overwintering pits and spawning grounds.

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