Measurement and Management of Fish Spawning Habitat Effectiveness Considering Potential Migration Barriers

With an increasing focus on ecological conservation, protecting and restoring spawning habitats for migratory species has become a focus of attention. However, restoration designs focusing only on increasing the quantity of spawning habitats for fish can result in little to no improvement, as the presence of various potential barriers would severely impede fish from accessing upstream habitats and utilizing their resources, thus further affecting the effectiveness of restoration efforts. Here, we suggest a more comprehensive assessment framework which closely links potential barriers and upstream migration opportunities with the quantity and quality of fish spawning habitats. This framework was implemented to assess the influence of potential migration barriers on the availability of spawning habitats in order to enhance the pertinence and effectiveness of river restoration technologies. In this study, we used the Heishui River, a primary tributary of the Jinsha River, as a case study to research the distribution of fish potential migration obstacles under hydropower development, and restoration efforts were designed to coordinate the accessibility and quality of spawning habitat, which was beneficial for increasing the restoration success probability. The results showed that neglecting river potential barriers would lead to overestimation of fish spawning habitat effectiveness. The effective spawning habitat (ESH) determined by considering potential barriers was reduced by 54.0%–86.9% (for Schizothorax wangchiachii) and 31.4%–86.9% (for Jinshaia sinensis) compared with the traditional weighted usable area (WUA) thus may lead to the deviation of ecological restoration patterns and effects. We highlight that, in the river ecological restoration targeting migratory species, priority should be given to potential barriers restoration close to the downstream estuary and those areas with poorer habitat quality, so as to ensure the effectiveness of more and better-quality spawning habitats. The proposed framework can help managers in conducting sustainable assessments and conservation of potential habitats while informing decisions on habitat restoration priorities.