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].