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.