Changes in fish assemblages following the implementation of a complete fishing closure in the Chishui River

The Chishui River is the first to have a complete fishing-closure in the Yangtze River basin. To explore how fish assemblages changed following the implementation of the fishing closure, field surveys were conducted biannually in three reaches (upper, middle and lower) along its longitudinal gradient during 2007 to 2019. A total of 143 species from eight orders and 24 families was collected. Diversity index for all three reaches showed no significant changes through time. However, non-metric multidimensional scaling (NMDS) ordination analysis revealed significant temporal changes in the structure of fish assemblages for all reaches (P<0.05 in all cases). Time-lag analysis further showed that the fish assemblages in the upstream had reverted to the early study periods (P 0.05), with the relative abundance of some large-sized species (e.g., Onychostoma simum and Spinibarbus sinensis) returning to former levels immediately after fishing closure. Fish assemblages in the midstream and downstream reaches also showed trends to returning to the early study periods, but did not reach statistical significance (P 0.05). These discrepancies might be attributed to varying human disturbances and the type of fish species composition along the longitudinal gradient.

Automated summary

The Chishui River implemented a complete fishing closure, during which the diversity index of fish assemblages showed no significant changes, but the structure of fish assemblages changed significantly over time. The upstream fish assemblages reverted to pre-closure levels, while the midstream and downstream fish assemblages also showed a trend of recovery.