Stock assessment and management implications of an endemic fish, Oxygymnocypris stewartii, in the Yarlung Zangbo River in Tibet, China

Abstract

Abstract Background Oxygymnocypris stewartii is an endemic species only inhabiting the middle and upper reaches of the Yarlung Zangbo River and its tributaries at altitudes above 3600 m in the Qinghai-Tibet Plateau and has suffered a continuous decline of population size owing to anthropogenic disturbance. However, little is known about the stock status of this species and how to protect it. In this study, we evaluated the population status of O. stewartii and investigated two management policies including the minimum age limits and seasonal closure in the Yarlung Zangbo River. Results Estimates of the total mortality rate were 0.35 year−1 for females and 0.65 year−1 for males. The natural mortality rates were estimated as 0.10 and 0.22 year−1 for females and 0.12 and 0.29 year−1 for males using two empirical methods. The O. stewartii population may be in near full exploitation under the current harvesting strategy in the Yarlung Zangbo River, with a high chance of recruitment failure in the future. Although both minimum age limits and seasonal closure could be effective measures to conserve the O. stewartii stock, it was proposed that a seasonal closure was implemented each year from September to December according to the complexity of the application and the effects on the income of local fishermen and on the biological invasion. Conclusions The stock of O. stewartii may be in near full exploitation under the current harvesting strategy, with a high chance of recruitment failure in the future. Our results indicated that the imposition of the seasonal closure from September to December might be the effective measure to conserve the O. stewartii population.