Climate change drives contrasting shifts in fish species distribution in the Mekong Basin

Abstract

Global changes are causing significant alterations to terrestrial, marine, and freshwater ecosystems worldwide, with substantial implications for plant and animal populations, potentially leading to species extinctions. While freshwater ecosystems are recognized as particularly vulnerable to these impacts, there has been limited research conducted in tropical regions on how these changes will affect them. Here, we assessed the relative impacts of change in climate and human population density on fish species distribution between current (1970–2000) and future (2050s) time periods in the Mekong River. We analyzed occurrence data for 195 fish species from 10 functional guilds and employed species distribution models (SDMs) to evaluate potential changes in fish species distribution under the independent and combined impacts of changes in climate and population density. Our results show that climate change, with significant change in temperature and precipitation rather than minor population shifts, will be the primary driver of future change in fish species distribution in the Mekong River with all fish guilds likely to expand their suitable habitats. However, contrasted distributional changes were observed among fish species, with certain guilds projected to gain more suitable habitat than others. Out of the 195 species examined, the majority of fish species studied (i.e., 84 %) are expected to undergo a northward distributional shift, while 49 species may experience a reduction in their suitable habitats. Additionally, significant declines in species richness are projected to occur in currently diverse areas (i.e., Tonle Sap Lake and River), while the highest increases in fish species richness are projected to occur in the 3S (Sesan, Sekong, and Srepok) River Basins. These findings highlight potential hotspots for mitigating the impacts of environmental changes, providing an opportunity for conservation practitioners and planners at the national and regional levels to develop and implement adaptation and mitigation measures.