Importance of peripheral basins: Implications for the conservation of fish assemblages

Abstract

Abstract The upper Dniester River basin (Black Sea basin) contains unique fish assemblages. Although data on the fish of the basin are scarce, evidence indicates that these assemblages have declined. It was assumed that the peripheral basins (i.e. small basins on the edge of the larger basin) of the upper Dniester River basin could maintain good ecological status. To fill the knowledge gaps and assess the role of peripheral basins on fish species and assemblage conservation, research was conducted in the Strwiąż River basin. Data from the Strwiąż basin and the adjacent but unconnected upper Wiar basin (the Vistula basin; Baltic Sea basin) were compared in order to examine the influence of historical factors, and to confirm the unique characteristics of the fish assemblages of the peripheral area of the upper Dniester basin. A detailed analysis of the fish assemblages was performed, the primary morphological characteristics of sites that corresponded to the requirements of the fish assemblages were defined, and the human impacts were identified. The Strwiąż River basin is likely to be the only fragment of the upper Dniester basin with a well‐preserved fish assemblage. It features high species richness and numerous native Ponto–Caspian species that function near the edge of their ranges. The extant fish fauna of the Strwiąż River basin can provide a point of reference for other tributaries of the upper Dniester River that are degraded. We draw attention to the fact that peripheral basins, which are not usually considered in conservation biogeography, can be important for the protection of fish species and entire fish assemblages. This study provides one of the most convincing arguments for a more detailed investigation of peripheral populations.