Prospects for conserving freshwater fish biodiversity in the Anthropocene: A view from Southern China

Abstract

Globally, population declines of freshwater animals have been consistently greater than counterparts in other realms, making fresh waters hot spots of endangerment—particularly for larger species. Furthermore, biotas have become increasingly homogenized as invasions by non‐native species proceed. These trends are particularly evident in Anthropocene China, where humans have profoundly altered freshwater ecosystems, with serious consequences for fishes and other aquatic vertebrates. Here, I examine the prospects for ‘bending the curve’ or reversing the trend of freshwater fish biodiversity loss in China, focusing on examples from the Yangtze and further south. Much of China's rich fish biodiversity is threatened, but a lack of contemporary surveys means that the conservation status of many species is uncertain, and ~40% of fishes are data deficient. Although nutrient pollution of major rivers has abated recently, poor water quality remains a concern, and the widespread proliferation of emerging contaminants and microplastics can be expected to have unpredictable (but detrimental) effects on the biota. Warmer temperatures will exacerbate the toxicity of micropollutants, and facilitate the spread of non‐native species that have been supplanting native fishes. Extensive dam construction has fragmented major rivers, and has blocked fish migrations, preventing access to spawning sites and leading to population extirpations. Dams limit the ability of fishes to adjust their ranges to compensate for global warming, with increased drought severity and frequency under climate change representing an existential threat. Overexploitation will be reduced by the recent introduction of a 10‐year fishing ban in the Yangtze basin, but dams, flow regulation, emerging contaminants and continuing habitat degradation will stymie any population recovery or significant recovery of biodiversity as a result of the ban. Furthermore, captive breeding and release programmes have failed to restore populations of threatened fishes because poor management of breeding stock has allowed inbreeding or hybridization leading to genetic pollution of wild populations. Other anthropogenic activities, such as large‐scale mining of river sand on the Yangtze flood plain—exacerbated by the sediment‐trapping effects of upstream dams—are persistent obstacles to reversing the trend of fish biodiversity loss in China.