Drivers and mitigation of capture-induced damage in glass eels (Anguilla japonica): empirical evidence from China’s east coast

Overfishing and coastal environmental alteration threaten recruitment of the migratory Japanese eel ( Anguilla japonica ), and unrecorded losses from capture-induced damage may undermine fishery sustainability. Using empirical monitoring data from China’s eastern coast, we evaluated the capture-induced damage rate (CIDR) as a practical ecological indicator for glass eel protection by characterizing its spatiotemporal dynamics, quantifying the combined effects of environmental (temperature, tide) and fishing (effort, net type) drivers, and deriving actionable thresholds and adaptive strategies to reduce concealed losses. CIDR showed marked spatiotemporal variability, with elevated risk concentrated within the recruitment season. Damage increased nonlinearly with fishing effort and was strongly amplified at higher temperatures, identifying 15 - 22 °C as a critical risk interval. Neap tides were associated with a marginally higher CIDR than intermediate tides, while protector installation effectively reduced damage; under the “spring tide + protector” scenario, CIDR decreased by 14.3% (medium effort) and 61.8% (high effort), corresponding to 15.16 and 65.71 fewer damaged glass eels per 1,000 m 2 , respectively. The safe upper limit of fishing effort for rotating nets was estimated at 5.7 × 10 3 m 2 , with 100% compliance in the observed data set. We propose an adaptive management framework that integrates real-time temperature/tide data, dynamic effort adjustment, and mandatory protector use to keep CIDR within a safe range. Future research should validate the indicator’s applicability across different marine regions and refine thresholds to enhance the sustainability of eel fisheries and coastal ecosystem governance.