Temporal Dynamics and Evidence of Declining Fish Diversity in Lake Sarysu, Azerbaijan (1967-2021)

Abstract

Lake Sarysu, the largest natural lake in Azerbaijan, is a key freshwater ecosystem in the Kura-Aras Lowland. This study quantified long-term changes in fish species richness and community composition across a 54-year period, from 1967 to 2021, by integrating published historical records from three survey periods with recent field surveys conducted in 2020-2021. A total of 30 fish species were recorded across all periods, nine of which were consistently observed. Species richness increased from 15 species in 1967-1972 to 25 species in 2009-2015, followed by a 44% decline to 14 species in 2020-2021. The partitioning of S & oslash;rensen dissimilarity indicated that earlier temporal differences were primarily associated with species turnover, whereas nestedness-resultant dissimilarity dominated the most recent change, which is consistent with net species loss. Hierarchical clustering separated the two most recent periods from the earlier periods, indicating a marked temporal change in the documented assemblage. Overall, these results document a recent contraction in fish diversity and provide a baseline for future monitoring and management of Lake Sarysu.