Zoning effects on fish populations in a key Chinese multi-use marine protected area

Multi-use marine protected areas (MMPAs), characterized by zones with varying levels of protection, are increasingly recognized as essential fishery management tools. However, comprehensive understanding of their zoning impacts remains limited. This study investigates the effects of zoning on fish populations within Shengsi Marine Park, a prominent MMPA in the Yangtze River Delta known for its significant resource utilization and human intervention. Using Generalized Additive Models (GAMs), we evaluated how zoning influences fish community characteristics, hypothesizing that higher protection level zones and their adjacent areas would show increased values across various fish community indicators. Our results partially supported this hypothesis: total species richness and the biomass of low commercial importance (LCI) species tended to be highest in the highest protection level zone. In the second protection level zones, only the biomass of high commercial importance (HCI) species was tended to be higher than that in the third protection level zones. Notably, zones adjacent to the highest protection level zone showed enhanced biomass of HCI fishes, indicating potential spillover effects. The relative influence of zoning varied across ecological indicators: the mean size of moderate commercial importance (MCI) species demonstrated the highest relative influence at 18.86%, followed by total species richness at 15.49%, and the mean size of all species at 14.81%. In contrast, total abundance had the lowest influence at 0.03%, with LCI abundance and biomass at 0.03% and 0.18%, respectively. While zoning significantly influenced both HCI and LCI species, the impacts were more pronounced for HCI species, further supporting our hypothesis regarding differential impacts based on commercial importance. Multivariate analyses indicated that zoning explained 7% of species assemblage variation. Pairwise comparisons highlighted significant differences between third protection level zones, with Cynoglossus lighti emerging as the most influential species, contributing 9% to total zone dissimilarity. This study provides novel insights into the ecological effects of zoning in Chinese MMPAs and underscores the potential of MMPAs as effective spatial management tools that integrate marine conservation and fisheries management.