Spring climate warming is associated with earlier spawn timing of an adfluvial trout population

Phenological shifts are being observed in salmonid fish in response to
climate change. Between 1961 and 2021, daily spawner counts have taken
place during the spawning season, and climate and hydrologic measurements
have been measured continuously near the spawning site for Gerrard Rainbow
Trout in British Columbia, Canada. Trend and multiple regression analysis
was conducted to determine phenological shifts and associated climate and
hydrology metrics. Over the 61-year time series, the timing of peak
spawning shifted earlier by 7.7 days and the duration of the spawning
period shortened by 12.3 days due to the spawning season ending earlier;
the timing of the start of the spawning season did not change. The shift
in peak spawn timing was associated most strongly with an increase in
early spring (March-April) air temperature (2.2 °C), an increase in water
temperature (1.3 °C), and less strongly with hydrology metrics.
Mountainous regions are experiencing earlier and warmer springs. Adfluvial
trout populations in these regions such as Gerrard Rainbow Trout may be
remaining resilient at least partially through adaptation of phenology.