Habitats of freshwater cetaceans are under increasing threats of deterioration globally. A complete understanding of long-term variations of habitat configurations is therefore critical. Poyang Lake in China contains a large and stable population of the Yangtze finless porpoise, a critically endangered freshwater cetacean species. However, constant water decline and intensified human activities in the lake since 2000 have led to uncertainty for porpoise conservation. We address this issue via remote sensing and hydrodynamic modeling of nine environmental variables during different seasons over the past two decades. The MaxEnt model was used to extrapolate changes in likely habitat configurations of the porpoise, and MARXAN algorithms delineated habitat protection priorities in different seasons. Results illustrate that flow velocity, water depth, Chl-a concentration, distance to grassland and boats greatly affect the porpoise distribution. Shifts in these environmental variables can lead to significant habitat decreases in all seasons. In particular, unstable hydrological regimes may force the porpoises to live in habitats with lower water depths for suitable flow velocity conditions in the dry season, and habitats are increasingly infringed by grassland and mudflats. High protection priority areas such as the northern channel and the estuaries of the tributaries urgently need long-term systematic and targeted surveys of ecosystem functionality and flexible management of anthropogenic activities. Combining remote sensing with hydrodynamic and species distribution models can also assist in understanding the situation of other aquatic species.
Keywords: Freshwater conservation planning; Habitat configuration variation; Habitat degradation; Hydrodynamic modeling; Remote sensing; Species distribution modeling.
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