Study on the early resource status of Gymnocypris przewalskii in Qinghai Lake and its relationship with the environment factors

Background The early-life stage resources (fertilized eggs and larvae) of Gymnocypris przewalskii are particularly crucial for population recovery and provide an important basis for the conservation and management of current fishery resources. Objective This study investigates the relationship between the status of G. przewalskii early-life stage resources and environmental factors in the main inlet rivers of Qinghai Lake, aiming to provide a scientific basis for the protection of its early resources (larvae and fertilized eggs ) and for the ecological scheduling of water conservancy projects. Methods From 2018 to 2024, monitoring was conducted annually from June to September. Based on the actual conditions of each river, conical nets were deployed at monitoring sections in the Buha River, Shaliu River, Quanji River, Heima River, and Ha’er River to monitor early resources. Monitoring was performed 3 times per month, with 12 sampling sessions each time, lasting 24 hours. Additionally, routine monitoring was carried out in the Buha River from June to September, with one session each in the morning, noon, and evening daily. Results From 2018 to 2024, the Buha River recorded a total of 6 082 larvae and 2 671 fertilized eggs, with an average drifting density of (7.6×10^-1±0.61) ind (grains)/m³ and a cumulative resource amount of 20.22×10⁸ ind (grains). The Shaliu River recorded 14 962 larvae and 6 777 fertilized eggs, with an average drifting density of (2.0×10^-1±0.09) ind (grains)/m³ and a cumulative resource amount of 1.89×10⁸ ind (grains). The Quanji River recorded 163 339 larvae and 6 791 fertilized eggs, with an average drifting density of (6.5×10^-1±0.49) ind (grains)/m³ and a cumulative resource amount of 2.55×10⁸ ind (grains/larvae). The Heima River recorded 6 082 larvae and 5 359 fertilized eggs, with an average drifting density of (1.07±0.49) ind (grains)/m³ and a cumulative resource amount of 0.22×10⁸ ind (grains). The Ha’er River recorded 7 365 larvae and 3 531 fertilized eggs, with an average drifting density of (1.5×10^-1±0.06) ind (grains)/m³ and a cumulative resource amount of 0.82×10⁸ ind (grains). In June, fertilized eggs accounted for 94.2%—98.3% of the total number of fertilized eggs and larvae. In July, the numbers of fertilized eggs and larvae tended to balance, while in August, fertilized eggs accounted for only 0.1%—9.6%. Significant commonalities were observed in the diurnal rhythms of larvae and fertilized eggs across the five rivers. Specifically, the patterns for larvae were highly consistent, whereas those for fertilized eggs exhibited a “partially consistent, partially irregular” characteristic. The primary environmental factor influencing the abundance of early-life stage resources was light intensity (P<0.01). Conclusion The Buha River is the primary site for the occurrence of G. przewalskii early-life stage resources, while the Shaliu River and Ha’er River serve as important supplementary sources. Larvae exhibit a distinct diurnal rhythm, predominantly occurring at night. Light intensity is the key environmental factor influencing the abundance of early-life stage resources. The findings of this study provide scientific support for the sustainable ecological development of the Qinghai Lake fishery.