Materials and Methods
Study species and study area
G. przewalskii , Qinghai Lake naked carp, a short-distance anadromous fish, is the predominant species in Qinghai Lake34. In Qinghai Lake, G. przewalskii needs more than 7 years to reach sexual maturity, and then its breeding group seasonally migrates to inflowing rivers to spawn over sandy gravel beds when the river water temperature rises to 6~17.5°C from April to July 30. The length of inflowing rivers is shorter than 290 km, and the migration distance of G. przewalskiiis mainly 3 km to 120 km.
Qinghai Lake (N36.51°–37.25°; E99.58°–100.79°), the largest inland saltwater lake in China, is located on the Qinghai-Tibetan Plateau. The Qinghai-Tibetan Plateau, named the third pole, is one of the most sensitive regions to global warming on Earth 35-37. The average annual air temperature on the plateau increased by 0.319 °C/10 y during 1987-2016, whereas the value was 0.415 °C/10 y from 2005-2016 29. From 1979 to 2016, in Qinghai Lake, the freeze start date and freeze completion date were pushed back by 6.16 days and 2.27 days, respectively, while the ablation start date and ablation completion date advanced by 11.24 days and 14.09 days, respectively 28.
Data collection
We monitored the arrival dates of G. przewalskii breeding population migrated into the main spawning grounds (the reach between the railway bridges and highway bridges) of three main inflowing rivers (Buha River, Quanji River and Shaliu River) during 2014-2020. We monitored the breeding population size and larval flux of G. przewalskii in the main spawning grounds of the three main inflowing rivers during 2018-2020. From 2018 to 2020, there were 7 surveys in Qinghai Lake near the Buha River estuary in which G. przewalskiiwas captured using gill nets, and each individual was dissected to identify its stage of gonadal development. We collected the discharge records of the three main inflowing rivers from 2018 to 2020. We collected air temperature records from Gangcha during 2011-2020.
Data analysis
We compared the migration rhythm variation of G. przewalskii with the variations of air temperature and river discharge to identify whether and how environmental variations impacted the migration phenology of G. przewalskii . We compared the migration rhythm variation of G. przewalskii with the gonadal development rhythm variation of G. przewalskii to identify whether there was a mismatch between migration rhythm and gonadal development rhythm. We analyzed the breeding population size and larval flux of G. przewalskii in the main spawning grounds of the three main inflowing rivers to identify whether the species was threatened.
Acknowledgements: This work was supported by the Natural Science Foundation of Qinghai [grant numbers 2018-ZJ-908]; and the National Freshwater Fisheries Germplasm Resources Conservation Bank Project [grant numbers FGRC-18537].