Fishes of the Salgir River in Modern Realities: Anthropogenic Impact and Invasive Species

The fish fauna of small mountain and foothill rivers of Crimea is currently undergoing significant changes. The main factors determining these processes are the penetration of alien species, active exploitation of rivers by humans, and modification of the Crimean hydrographic network associated with the North Crimean Canal. All this necessitated an assessment of the current state of the Salgir River ichthyofauna. In the period from 2010 to 2014 and in 2023, 2465 fish specimens were sampled in four areas of the river. A decrease in species diversity was revealed, especially pronounced in the upper reaches of the Salgir River (from 11 to 7 species), where the invasive species Alburnoides maculatus (Kessler, 1859) was a stable superdominant. The proportion of other alien species also increased from 1.5 to 13.1%. In the transition area between the upper and middle reaches of the Salgir River, extremely low numbers and diversity of fish communities have been recorded. A change in the species composition was noted here: the previously common minnow Phoxinus phoxinus (L., 1758) (70%) was replaced by the chub Squalius cephalus (L., 1758) and the gudgeon Gobio krymensis Bănărescu & Nalbant, 1973. Invasive species were occasionally encountered—the pumpkinseed Lepomis gibbosus (L., 1758) (25.0%) and the bleak Alburnus alburnus (L., 1758) (1.95%), but the previously common shemaya A. mentoides Kessler, 1859 and the Crimean barbel Barbus tauricus Kessler, 1877 were absent. The elimination of the rheophilic native species—the stone loach Barbatula barbatula (L., 1758)—was recorded. In the direction from the upper to the lower reaches of the river, the indices of species richness and evenness increased, and the dominance index decreased. An improvement in the diversity of fish population in the lower reaches of the river was noted, but it should be taken into account that they are represented mainly by alien species, the proportion of which varied from 80.9 to 98.7% (on average 89%).