Threatened salmon rely on a rare life history strategy in a warming landscape

Abstract

Rare phenotypes and behaviors adopted by only few individuals in a population are often overlooked, yet they may serve a heightened role for many organisms coping with warming climates. In threatened spring-run Chinook salmon spawning at the edge of the species range (Central Valley, CA USA), latemigrating juveniles were critical to cohort success in years characterized by multi-year droughts and ocean heatwaves. Late migrants rely on cool over-summer river temperatures, and are thus increasingly rare due to the combined effects of warming and dam construction. Yet our results suggest, the further loss of this within-population diversity could have critical impacts to their persistence in a warming climate. Our modeling predicts that thermally appropriate river conditions to support this phenotype will shrink rapidly in the future, and will primarily occur above impassable dams. Importantly, while late migrants dominated returns in some years, interannual variability in individual growth rates and migratory strategies suggests the importance of portfolio effects for these at-risk populations.Reconnecting and maintaining diverse habitat mosaics to support phenotypic and phenological diversity will be integral to the long term persistence of this species.

Intraspecific variation in migration timing of green sturgeon in the Sacramento River system

“…River residents have been described for other sturgeon species, including lake sturgeon (Borkholder et al, 2002; Colborne et al, 2019; Rusak & Mosindy, 1997) and shortnose sturgeon ( Acipenser brevirostrum ; Kynard et al, 2009). Furthermore, alternate migration strategies are a common aspect of salmonid biology in California, presumably as a bet‐hedging adaptation for the variable Mediterranean climate (Cordoleani et al, 2021; Prince et al, 2017; Thompson et al, 2020). Even though some of the green sturgeon monitored in this study spent over a year in the Sacramento River, they all eventually returned to the Pacific Ocean and on average returned to the river on a 4‐year cycle (see Appendix S1: Figure S1).…”

Considerations for the Development of a Juvenile Production Estimate for Central Valley Spring-Run Chinook Salmon

“…Otoliths (calcareous structures in the inner ear) can provide information on fish age, habitat-specific growth rates, duration of freshwater rearing, fish size at out-migration, and migratory histories. Otoliths from adult carcasses recovered on spawning grounds can provide these metrics for successful spring-run escapees (Barnett-Johnson et al 2008;Johnson et al 2017;Cordoleani et al 2021). This is because ratios of environmental strontium vary predictably for many locations across Central Valley watersheds and are incorporated into the daily layers in otoliths, providing a record of their movements across the landscape over their lifetime (Ingram and Weber 1999;Barnett-Johnson et al 2008).…”

“…This is because ratios of environmental strontium vary predictably for many locations across Central Valley watersheds and are incorporated into the daily layers in otoliths, providing a record of their movements across the landscape over their lifetime (Ingram and Weber 1999;Barnett-Johnson et al 2008). Significant insights into ecology and behavior have been revealed using this approach Phillis et al 2018;Sturrock et al 2020;Cordoleani et al 2021).…”

“…Recent work by Cordoleani et al (2021) revealed the demographic value of yearling spring run to the viability of Mill and Deer creek populations; this may need to be considered in the context of the JPE. For example, during multi-year droughts and ocean heat waves, late yearling migrants that left the freshwater during cooler fall conditions were the only survivors to adulthood.…”

Climate Change Impacts on San Francisco Estuary Aquatic Ecosystems: A Review

“…Chinook Salmon typically benefit from wetter years and suffer in drought years (Munsch et al 2019(Munsch et al , 2020. However, Chinook Salmon demonstrate high life-history diversity and phenotypic plasticity (e.g., Crozier et al 2008;Goertler et al 2018), which buffer the species from various detrimental conditions (Cordoleani et al 2021). Nevertheless, human actions have weakened the overall complexity of Chinook Salmon populations in the Central Valley, though efforts are underway to mitigate such effects (Carlson and Satterthwaite 2011).…”