Larval drift and dispersal are critical processes that affect recruitment success for many riverine fishes. Hypolimnetic discharge from the Three Gorges Dam (TGD) lowers river temperature and reduces downstream nutrients, inducing distinct shifts in habitat conditions downstream of the dam. The inflow of major tributaries buffers these influences and creates physiochemical gradients according to the distance from the dam. We investigated the abundance, feeding, and growth of larvae of four major Chinese carps in three sections of the middle Yangtze River. Water temperature and transparency showed clear spatial gradients. Larvae in the river section closest to the dam tended to be lower in abundance and temporally delayed peak abundance and showed lower feeding intensity, poorer condition, and slower growth than those further from the dam. Our results demonstrate that physiochemical gradients influenced by the TGD have strong effects on abundance, feeding, and growth of the drifting larvae. We recommend that river sections farther from the TGD, particularly around the mouth of Poyang Lake, should become high-priority conservation areas to enhance protection of critical aquatic species.

Drifting larval fish assemblages were investigated at three sections in the middle reach of the Yangtze River downstream of the Three Gorges Dam to reveal recovery gradients and to identify the major environmental factors influencing their temporal and spatial patterns. Larval fish in the river section closest to the dam showed lower abundance, later occurrence, narrower temporal niche breadth, and more pairs of dominant species with high niche overlap than those further from the dam. Water temperature, transparency, and discharge significantly influenced the larval fish assemblages. They showed longitudinal gradients of increased water temperature, decreased transparency, and increased discharge in a downstream direction. Our results suggested that hypolimnetic and clean water discharge from the dam heavily impacted larval fish assemblage in the river section near the dam. With an increased distance to the dam and the input of some major tributaries, this impact was gradually buffered, thus forming the longitudinal recovery gradients. We suggest that priority for conservation should shift from river sections closer to the dam to those further from the dam.