Comparative Population Dynamics of Schizothorax wangchiachii (Cyprinidae: Schizothoracinae) in the Middle Reaches of the Yalong River and the Upper Reaches of the Jinsha River, China

SIMPLE SUMMARY: Ecological characteristics of the two economically important Schizothorax wangchiachii populations from the upper Yangtze River were compared. Their age structures were similar, but the growth coefficient, initial sexual maturity age and age at first capture were significantly different between the two populations. Both populations were in an overfishing state due to the current fishing intensity. These results can provide information for planning additional resource protection for Schizothorax wangchiachii. ABSTRACT: To explore the differences in the growth characteristics and population dynamics of Schizothorax wangchiachii populations in the Jinsha River (JSR) and the Yalong River (YLR), samples were collected in the upper reaches of the JSR (n = 230) from 2019 to 2020 and the middle reaches of the YLR (n = 187) from 2017 to 2018. In the JSR and YLR populations, the age range was 11 and 12 years old, respectively, and the best growth equation was the Von Bertalanffy equation. The comparative analysis of the two populations showed that the growth coefficient, initial sexual maturity age and age at first capture of the YLR population were greater than those of the JSR population. Comparing the mortality rates of the two groups, we found that the YLR population had the higher female mortality rate (0.658 years(−1)) and the lower male mortality rate (0.453 years(−1)). Our assessment of the three natural mortality rates showed that the F(cur) of both male and female populations was greater than F(25%), indicating that both populations were in an overexploited state. Therefore, we suggest considering the two groups as separate protection units and implementing management measures such as ecological regulation, restoration of tributary habitat and strengthening of fishing ban monitoring to protect their resources.