Shoreline hardening affects species composition and condition of larval fishes in the Yangtze River: Implications for conservation and inshore habitat restoration

Inshore habitats play a crucial role in the downstream drift of larval fish in large rivers. Natural inshore habitats of most of the world's large rivers have been heavily degraded by shoreline stabilization measures, but the knowledge about consequences for the condition and distribution of larval fishes is extremely limited. Investigations during the peak season of larval drift into species composition as well as into feeding intensity and body injuries of representative taxa were conducted at different inshore mesohabitats along semi-natural and stabilized shores in a free-flowing section in the middle Yangtze River. Species were unambiguously identified by a combination of DNA barcoding and morphological analyses. Overall, 37 taxa from seven families were detected from a total of 9,915 fish larvae caught. Earlier developmental stages greatly outnumbered the later stages in diversity and abundance in each investigated mesohabitat. Abundance and assemblage structure as well as the body injury rate differed significantly between mesohabitats. Generally, overall species richness and abundance tended to be lower, and divergence of the assemblage and body injury rates tended to be higher at heavily hardened shores, which could be contributed to the poor riparian vegetation and restricted suitable hydraulic conditions there. Our results may reflect the underestimated impact of inshore habitat degradation on larval fishes and highlight the demand for creating adequate areas of shallow and slow-flow habitats with good riparian vegetation conditions along the shores. These measures will foster an appropriate connectivity between spawning areas and high-quality nurseries for larval fishes.