Conservation and restoration of riverine spawning habitats require fine-scale functional connectivity and functional heterogeneity

A severe extinction crisis of migratory fish caused by extensive hydropower development and climate change has attracted widespread environmental concern. Conserving and restoring riverine spawning habitat for migratory spe-cies is advantageous for population recovery. Depending on the reproductive characteristics of fish with adhesive eggs, functionally heterogeneous spawning habitats are required to support different stages of reproductive activity. However, few aquatic assessment models are available to consider the fine-scale functional connectivity between het-erogeneous spawning habitats. This study developed a function-based framework that linked fine-scale functional con-nectivity modeling to habitat quality evaluations for the population recovery of migratory fish. The function path tree (FPT) model within the framework could identified the spatiotemporal dynamics of fine-scale connectivity patterns by emphasizing the attribute-dependence of patch arrangements. Here, we used the Chinese sturgeon, a well-known endangered anadromous fish producing adhesive eggs in the Yangtze River, as an example to demonstrate the appli-cability of the framework. Additionally, the ecological effectiveness of river restorations to overcome the detrimental influence of climate change on discharge decrease was also investigated. Compared to prior research, our methodology effectively enhanced the predictive performance of spatiotemporal distributions and quality assessments of spawning habitats. A strong correlation was discovered between the ecological profit indicator (HQI) and the estimated fecun-dity (R2 = 0.941) and field-collected eggs (R2 = 0.918). The minimum spawning discharge decreased from 8400 m3/s to 7000 m3/s by substrate restoration, with the optimal HQI growth rate of 52.7 % at Q < 8400 m3/s. This work will optimize long-term conservation for imperiled migratory species and help develop strategies to build resilience to ongoing environmental changes in flow-reduced rivers.

Automated summary

Extensive hydropower development and climate change have led to a severe extinction crisis for migratory fish, causing widespread environmental concern. This study developed a function-based framework to model fine-scale functional connectivity and evaluate habitat quality for the population recovery of migratory fish. Compared to previous research, our methodology effectively improved the predictive performance of spatiotemporal distributions and quality assessments of spawning habitats.