The impact of artificial reproduction and release on the native fish resources in the upper Yellow River: Taking the case of <italic>Gymnocypris eckloni</italic> in Longyangxia-Liujiaxia section as an example

<p indent="0mm">Over the past <sc>50 years,</sc> the population of <italic>Gymnocypris eckloni</italic> (Herzenstein, 1891) in the upper Yellow River has experienced a significant decline due to natural changes and human activities, which has severely limited the ecological and environmental protection and high-quality development in this region. Since 2009, the Longyangxia-Liujiaxia section (LLS) of the upper Yellow River has implemented artificial reproduction and release (ARR) measures for <italic>G</italic>.<italic> eckloni</italic>. However, quantitative analyses of the recovery effectiveness and potential optimizations of these measures are still lacking. In this study, based on population projection matrix theory and empirical fishery data, we constructed a population dynamic model for <italic>G</italic>.<italic> eckloni</italic> in the LLS, evaluated the individual growth characteristics and population resource changes before the start of ARR in 2008 and experiencing the ARR in 2016, and analyzed the effects of constant versus non-constant ARR strategies on the population recovery process. The results indicated that after <sc>9 years</sc> of ARR (2008–2016), the age structure of the <italic>G</italic>.<italic> eckloni</italic> population became younger, the average body size decreased, and the growth rates slowed, leading to a transition from a declining to a growing population status. Under the current constant release intensity <sc>(0.32 t/yr),</sc> 24, 48, and <sc>72 years</sc> were estimated for the <italic>G</italic>.<italic> eckloni</italic> population in the LLS to reach primary, advanced, and complete recovery goals, respectively; while under a constant total ARR, a non-constant release strategy with gradual annual reductions could effectively reduce the time costs to achieve these recovery goals, with distinct critical reduction thresholds for different recovery goals associated with minimizing the time costs. This study provides a scientific basis for the quantitative analysis of fish population dynamics, and offers theoretical and technical supports for conserving native fish resources in the upper Yellow River, promoting the sustainable development of the Yellow River basin.