Changes of cyprinid fishery resources in Lake Biwa over 57 years: association with multiple stressors and restoration measures.

Multiple stressors can threaten the resources of inland fisheries, but responses to these stressors may differ among fish species. We used a long-term fishery dataset to quantify the CPUE trajectories of eight cyprinid taxa in the south basin of Lake Biwa that have been stressed by lakeshore development, artificial water-level regulation, exotic fish species, and climate change. A Bayesian state-space model revealed that the CPUEs of all eight taxa substantially declined from 1966 to 2022. For Opsariichthys uncirostris, Ischikauia steenackeri, Sarcocheilichthys spp., Cyprinus carpio, and Carassius spp., the average population growth rates decreased from 1976 to 1991, when lakeshore development occurred and largemouth bass populations increased dramatically. For the three remaining taxa (Zacco platypus, Gnathopogon caerulescens, and Squalidus spp.), the average population growth rates decreased from 1992 to 2022, when new water-level regulations were implemented and bluegill populations increased substantially. The former five taxa exhibited longer maximum body length and life span, later maturation, and higher fecundity than the latter three taxa. This suggests that life-history traits may determine how species respond to different stressors. Unlike the effects of these three abrupt stressors, those of climate, a gradual stressor, were negative for seven taxa, although not statistically significant. We also found that the population growth rates of Gnathopogon caerulescens and Ischikauia steenackeri increased recently after implementation of restoration measures (fishing moratorium and stocking of paddy-reared/captive-bred individuals). Our results suggest that cumulative anthropogenic stressors depleted the resource of cyprinids but that the outcome of current restoration measures may be positive.