Comparative Assessment of the Current State of Semi-Anadromous and Non-Anadromous Fish Species in the Northern Part of Agrakhan Bay

Abstract

An unfavorable hydrological regime has contributed in recent years to negative changes in the species and age structure of the ichthyofauna in the northern part of the Agrakhan Bay of the Caspian Sea. The article presents the data on the species composition, age categories and morphometric indicators of semi-anadromous and freshwater fish species in detail based on the results of studies in 2019–2021. A comparative analysis of the obtained results with the data of previous years was carried out; negative dynamics of changes in the studied indicators under modern conditions were established. There has been a reduction in the species composition of semi-anadromous fish from 14 to 9 species, the commercially valuable kutum Rutilus kutum (Kamensky, 1901), catfish Silurus glanis (Linnaeus, 1758), vimba Vimba vimba (Linnaeus, 1758), tench Tinca tinca (Linnaeus, 1758) and asp Aspius aspius (Linnaeus, 1758) have disappeared, the share of the remaining surviving species has significantly decreased. The average age has increased, the proportion of fish of older age categories has grown, and, accordingly, the number of younger groups of fish has decreased, which indicates a decrease in growth potential. At the same time, freshwater low-value fish species such as crucian carp Carassius gibelio (Bloch, 1782), rudd Scardinius erythrophthalmus (Linnaeus, 1758), white bream Blicca bjoerkna (Linnaeus, 1758), and others have growth trends in terms of age and morphometric parameters.