The fine-scale functional connectivity process in rivers influences the fish natural reproduction

Dramatic environmental changes have altered the connectivity pattern of aquatic ecosystems and thus fish spawning habitats. Although connectivity processes in local riverine habitats are crucial for fish reproduction, existing connectivity simulation approaches do not allow for quantitatively describing the fine-scale connectivity structure driven by hydrogeomorphic variables. Here we proposed the fine-scale connectivity theory (FSCT) that tackled the challenge of nonlinearity issue in modeling asymmetric connectivity in water environments, aiming to clarify the mechanism of fine-scale functional connectivity structure on fish natural reproduction. The FSCT was applied to the spawning ground of the Chinese sturgeon, a critically endangered migratory fish of the utmost concern in the Yangtze River, China. Results demonstrated that our method outperformed present connectivity models with an accuracy improvement of 25.1%. This study revealed a high correlation between the connectivity of spawning habitats and spawning capacity of the Chinese sturgeon, with a value of 0.947. Our findings showed a significant decline in habitat connectivity within the Chinese sturgeon spawning ground since 2003, which was associated with the shift from an aggregated to a decentralized connectivity structure. This study can facilitate theoretical and technical support for habitat restoration and conservation efforts of endangered fish populations in dammed rivers.