Impacts of dams on fish habitat connectivity greatly outweigh climate change in the Jinsha river basin, China

In the context of the surge in hydropower development, the reduction in river network connectivity and the subsequent loss of biodiversity in riverine ecosystems has become a central topic of discussion. Current river connectivity assessments focus more on the physical structure connectivity of the river networks but rarely consider the survival needs of organisms. This study proposes a fish habitat connectivity method that integrates potential habitat distribution area and dendritic connectivity index (DCI) to establish the fish-specific river connectivity index (FCI). Four endemic fish living in different regions and with different ecological types (warm-water and cold-water fishes) in the Jinsha River Basin (JRB), China, were selected for spatial-temporal assessment of FCI. The effects of future climate change on FCI were also explored. Firstly, the DCIs for three periods (1970-2000, 2001-2020, and a future period) categorized by the number and scale of dam construction in the JRB were calculated. Then, the potential habitat distribution of target fish species under SSP126 and SSP585 scenarios for each period were projected using species distribution models. Finally, the FCIs, which consider climate change, dam construction, and species mobility, were derived by overlapping the DCI and habitat suitability index. The results show that the large-scale dam constructions in the mid-lower reaches of the JRB between 2000 and 2020 led to a significant decline in DCI, with only the headwater regions of the basin maintaining a DCI above 10%. Although suitable habitat would expand under the impact of climate change, habitat connectivity of all four fish species declined sharply over time with the future FCI falling below 10%. Dam construction had a greater impact on habitat connectivity than climate change. This study provides beneficial methods that comprehensively considers the factors of dam construction, climate change, and species mobility to evaluate the habitat connectivity for specific fish species and reveal the profound impacts of the dam construction on fish habitat connectivity to support for the protection of critical species in the context of water resources development and climate change.