In 2021, China imposed a ten-year commercial fishing ban on the entire Yangtze River — the most ambitious freshwater conservation experiment ever attempted. Five years in, the first comprehensive assessment has been published in Science. Fish biomass has increased 209 percent. Species richness has increased 13 percent. Larger fish — those over 7.5 inches — benefited most, consistent with the prediction that fishing pressure selectively removes large individuals, truncating the size distribution.
The Yangtze had been in decline for seventy years. Overfishing, pollution, and dam construction had reduced fish populations to a fraction of historical levels. The Chinese paddlefish — one of the world's largest freshwater fish — was declared extinct in 2020. The ban was controversial: it displaced hundreds of thousands of fishers and eliminated a significant food source. The question was whether removal of fishing pressure alone, without addressing dams or pollution, would be sufficient for recovery.
The 209 percent biomass increase in five years answers the question narrowly but clearly: removal of fishing pressure alone is sufficient for substantial population recovery, even with other stressors unchanged. The dams still fragment habitat. The pollution is still present. But fish populations recovered dramatically in response to a single variable change.
The structural insight is about bottleneck identification. The Yangtze's decline had multiple contributing causes, and multi-cause problems invite multi-cause solutions — address fishing, dams, and pollution simultaneously. The ban tested whether one cause dominated. It did. Fishing pressure was not one of several approximately equal stressors. It was the binding constraint. Removing it alone released enough capacity for a tripling of biomass.
This has implications beyond fisheries. When a system is in decline from multiple stressors, the instinct is to address all of them or to study their relative contributions before intervening. The Yangtze experiment suggests a different approach: identify the dominant stressor and remove it, even if other stressors remain. The system may recover enough to tolerate the remaining pressures. The perfect intervention is the enemy of the sufficient one.
The 13 percent increase in species richness, compared to the 209 percent increase in biomass, reveals another structural feature: populations recover faster than communities. Individual species can increase their numbers rapidly given reduced mortality. New species colonizing or recovering requires longer timescales — habitat reconnection, dispersal, establishment of breeding populations. The biomass number is the early signal. The richness number is the long-term trajectory.