Identification of suitable tributaries to compensate fish habitat loss in dammed rivers using environmental DNA metabarcoding

Using unregulated tributaries to compensate fish habitat loss in dammed mainstreams has recently been suggested as a promising strategy for river ecological restoration. One critical prerequisite is to find potential tributaries as alternative habitat, which depends on precise fish community surveys. In this study, both eDNA metabarcoding and electrofishing were used to characterise fish community compositions in the dammed lower Jinsha river and its tributaries (Heishui, Pudu, and Xiaojiang rivers) in China. The fish community composition detected by eDNA metabarcoding was consistent with that detected by the conventional method. Besides, metabarcoding has the advantage of detecting the presence of rare species with relatively low abundances. The non-metric multidimensional scaling showed that there was no significant difference in fish community composition between the mainstream and the Heishui river, while there was large difference in the fish community composition between the mainstream and other tributaries. The effectiveness of using the Heishui river as alternative fish habitat was verified by comparing the changes in fish communities before and after the impoundment of the mainstream. Taken together, this study indicates that eDNA metabarcoding is a viable method to identify the suitable tributaries which at least partly compensate for fish habitat loss in the dammed mainstream.