Freshwater protected areas (FPAs) are widely promoted as an important conservation tool for rebuilding overexploited fish populations and protecting aquatic habitats. However, passive fishing bans alone do not always lead to consistent ecological recovery, partly because non-native, stocked, and benthivorous fishes may also benefit from reduced fishing pressure and improved environmental conditions, potentially altering native fish communities and ecosystem processes. Yet, whether active fish removal can complement protection to enhance native biodiversity and ecosystem functioning remains poorly understood.

To address this gap, the research team led by Prof. GUO Chuanbo at the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences has made important advances in elucidating the effects of targeted fish removals (TFRs) on multidimensional native fish diversity and ecosystem functioning within freshwater protected areas. These advances have been published in the Journal of Applied Ecology.

In this study, the researchers conducted a comprehensive two-year field investigation across five Chinese lakes, comparing fish community dynamics between FPAs without removals and FPAs implementing TFRs. The removal treatments selectively targeted non-native, filter-feeding, and benthivorous fishes. Results showed that native fish taxonomic, functional, and phylogenetic diversity in FPAs without removals remained largely unchanged or declined, whereas TFRs significantly enhanced native taxonomic and functional diversity across multiple seasons. These findings indicate that targeted removals can complement passive protection and promote the recovery of multiple dimensions of native fish biodiversity.

Moreover, TFRs altered trophic relationships among fish, zooplankton, macroinvertebrates, and phytoplankton, strengthening the regulatory effects of fish communities on lower trophic levels. These changes were accompanied by reduced phytoplankton biomass and increased water transparency, suggesting that targeted fish removals can influence not only fish biodiversity but also broader ecosystem processes. Piecewise structural equation modelling further indicated that TFRs strengthened trophic regulation by fish communities, providing a potential mechanism linking fish community management to ecosystem functioning.

The effects of TFRs, however, were strongly context dependent. In Caohai Lake, where removals primarily targeted stocked filter-feeding fishes, non-native fish diversity increased while native functional and phylogenetic diversity declined, suggesting that removal of one fish group may generate niche opportunities for other non-native species. In contrast, in Erhai Lake, where removals primarily targeted non-native fishes, native fish abundance increased across taxonomic, functional, and phylogenetic dimensions. In addition, water-level management in Honghu Lake promoted fish emigration from protected areas, highlighting the importance of considering external environmental and management drivers when evaluating FPA outcomes.

These findings underscore the importance of integrating targeted and context-dependent active management with freshwater protected areas, particularly in systems affected by biological invasions, excessive stocking, or strong benthic disturbance. Rather than relying solely on passive fishing bans, combining protection with selective removal of ecologically disruptive fishes may provide a more effective approach for restoring native biodiversity, strengthening trophic regulation, and improving ecosystem functioning. This study provides important implications for refining freshwater conservation strategies and for the adaptive management of large-scale initiatives such as the Yangtze River “10-Year Fishing Ban.”

Effects of Targeted Fish Removals on Lake Fish Diversity Recovery and Ecosystem Functioning. (Image by IHB)

(Editor: MA Yun)