In a warming river, natural-origin Chinook salmon spawn later but hatchery-origin conspecifics do not

Abstract

Median timing of reproduction in salmonid populations is generally consistent among years, reflecting long-term patterns of natural selection from characteristics of the local environment. However, altered selection from factors related to climate change or human intervention might shift timing over generations, with implications for the population’s persistence. To study these processes, we modeled median timing of redd (nest) counts as an index of spawning timing by wild Chinook salmon in the Skagit River system in Washington State, USA. Over the last 2-6 decades, wild salmon have been spawning later by 0.03 – 0.52 d/yr, while a naturally spawning group that is influenced by strays from a hatchery has been spawning earlier by 0.19 d/yr. Trends in the spawning timing of hatchery strays may reflect opposing selection from the hatchery, where egg take for propagation has become earlier by 0.58 d/yr. As mean August river temperatures have risen over the period of record, hatchery timing trends may be moving in the opposite direction from the plastic or adaptive patterns expressed by wild fish.

Historical Records Reveal Changes to the Migration Timing and Abundance of Winter Steelhead in Olympic Peninsula Rivers, Washington State, USA

“…In the absence of this historical information, CHANGING WINTER STEELHEAD MIGRATION TIMING it appears that the diminished diversity in contemporary winter steelhead migration timing had generally become accepted as the norm, as previous assessments describe these runs as beginning in January, with the majority of fish migrating from March through May (Busby et al 1996;Johnson et al 1997;WDFW and Western Washington Treaty Tribes 2002;Cram et al 2018). Thus, the historical baseline for winter steelhead migration timing may be an especially important reference for population rebuilding efforts because, in addition to the demographic effects discussed previously, it underpins a population's adaptive capacity to keep pace with shifting climatic conditions, such as changing streamflow and temperature regimes (Reed et al 2011;Manhard et al 2017;Austin et al 2020). For example, winter steelhead tend to migrate and spawn earlier in warmer streams (Busby et al 1996;Brannon et al 2004), and if streamflows and water temperature regimes on the OP become more similar to those in more southerly climates (Wade et al 2013), then early migrating life histories may become increasingly important for population resilience.…”

“…A historical baseline could improve benchmarks for population attributes that are important for contemporary fishery management, such as migration timing and abundance (Ricker 1946;Hilborn 1985). For example, the timing of adult migration is highly heritable and sensitive to the timing and intensity of fisheries (Tillotson and Quinn 2018), but contemporary data spanning just a few decades may miss shifts in migration timing over longer time scales or that occurred prior to the onset of modern fisheries monitoring programs (Robards and Quinn 2002;Yoshiyama and Moyle 2010;Austin et al 2020). Changes in population abundance are also difficult to detect over relatively short time frames because trends can be obscured by estimate errors and high natural variability in ecological processes underlying fisheries data (Porszt et al 2012).…”

“…Historical data, described in detail below, spanned the period of circa 1948-1960, with occasional earlier records. Although several previous investigations have estimated historical abundances of Pacific salmon, changes in migration timing have received considerably less attention (Robards and Quinn 2002;Austin et al 2020). Filling this knowledge gap can be important for understanding abundance trends since reduced diversity in migration timing can negatively impact population resilience (Tillotson and Quinn 2018).…”

Quantification of thermal impacts across freshwater life stages to improve temperature management for anadromous salmonids

“…Therefore, while our results indicate that salmon spawned in locations in space and time that minimized each life stage’s mortality, reproductive success would likely have been even higher in the higher-elevation, cooler waters that were formerly exploited prior to the construction of major rim dams in the 20th century ( Beechie et al, 2006 ; FitzGerald et al, 2021 ; Lindley et al, 2004 ; McClure et al, 2008 ; Moyle et al, 2017 ; Myers et al, 1998 ). An additional consideration is that the populations in this study include natural- and hatchery-origin fish ( Moyle et al, 2017 ); hatchery fish may spawn at times or sites that yield lower survival relative to that of locally adapted, natural-origin fish ( Austin et al, 2021 ; Peterson et al, 2020 ), such that reducing hatchery influence within these populations may increase their survival.…”

“…However, three scenarios may increase survival for these potential spring-run populations. First, Chinook salmon can shift arrival or spawn timing to track environmental cues ( Austin et al, 2021 ; Peterson et al, 2020 ; Quinn et al, 2001 ) such that fish adopting a later arrival and spawning period than Clear Creek spring-run would likely experience lower mortality. Second, salmon will behaviourally thermoregulate to avoid high temperatures and other unsuitable conditions (e.g.…”