Study on the Structural Changes in Fish Communitiesfollowingthe Impoundment of Hydropower Stations in the Lower Reaches of the Jinsha River

This study focuses on the lower reaches of the Jinsha River (28°22′15″–28°39′16″ N, 104°03′27″–104°25′25″ E). Since 2008, the operation of a large-scale water control project in this area has led to the formation of a reservoir ecosystem, altering the hydrological conditions and exerting influence on the fish community structure within the reservoir. Long - term monitoring of fishery resources was conducted in 2006, 2008, 2010 - 2013 and 2016 - 2023. At the Shuifu sampling site in the reservoir area, 104 fish species from 8 orders and 24 families were recorded in total, including 20 Yangtze River upper - reach endemic fish species and 11 exotic ones. Fish functional groups are classified into four groups. The first group is the mid-upper and mid-lower water column migratory fish that prefer flowing water, including 16 species such as the Chinese barb and the Bairei minnow, accounting for 15.4%. The second group is the benthic migratory fish that prefer flowing water, including 30 species such as the round-mouthed copperfish, the long-finned gudgeon, and the Schizothorax prenanti, accounting for 28.8%. The third group is the sedentary fish that prefer still water, including 37 species such as the Ziliang gudgeon and the minnow, accounting for 35%. The fourth group is the sedentary fish that prefer flowing water, including 21 species such as the Wasi yellow catfish and the wide-finned catfish, accounting for 20%.Significant differences in fish assemblage structure were found between the pre - and post - reservoir operation periods (R=1.000, p=0.1%<0.01). The main fish species contributing to this difference are 14 species such as Parakysis vorax, Sinohypselobarbus wangi and Sinopseudes dabryanus, with each of their difference contribution rates exceeding 2%, adding up to a cumulative rate of 61.07%. In the catch, the resource abundance of rheophilic fish species and those needing flowing water for spawning (like Psephurus gladius, Schizothorax curator, Ophiogobius makimurai and Sinohypselobarbus wangi) has declined noticeably, while that of eurytopic fish species (such as Parakisis vorax, Parakisis parvus, Belontia signata and Hypophthalmichthys molitrix) has risen. It is recommended to enhance the habitat protection of key aquatic habitats in the backwater section of the reservoir area of a certain power station, implement ecological dispatching and restore the connectivity of important tributaries, and at the same time establish a long-term ecological monitoring network.