Contrasting life-cycle impacts of stream flow on two Chinook salmon populations

Abstract

Stream flow affects many aspects of freshwater fish biology, but the extent to which variation in stream flow influences productivity of anadromous salmonid populations across their entire life cycle is not well known. We compared relationships of stream flow and productivity for Chinook salmon (Oncorhynchus tshawytscha) from two systems in the Salmon River basin in Idaho: the Lemhi River, a watershed subjected to intensive water use for irrigation, and Marsh Creek, a drainage with a natural hydrograph. We estimated rates of productivity based on monitoring at four life stages: the number of eggs initiating each cohort, juveniles migrating from the natal tributary past an outmigrant trap, smolts surviving to the Snake River, and adults returning to spawn. Using model selection techniques, we examined whether river flow experienced during these life stages explained variation above and beyond predictors of climate associated with each stage. In the Lemhi River, tributary stream flow during early residence exhibited strong correlations with egg-trap, egg-smolt, and egg-adult return rates, and was consistently a better predictor of productivity than stream flow occurring during late summer. Model selection indicated that early rearing flow was the single best predictor of both egg-trap and trap-smolt transition rates in the Lemhi River, and path analysis revealed a strong set of pathways linking rearing flow to adult return rate primarily through egg-trap productivity. These patterns were much less strongly exhibited or nonexistent in Marsh Creek. However, for both populations, migration flow in the Columbia River was the best predictor of smolt-adult return rates. Potentially confounding climatic variables exhibited relatively weak effects upon both early life histories and tributary flow, but were included in the best models of migration flows and smolt-adult return rate. These results suggest that effects of stream flow on juvenile salmonids in flow-altered systems can have substantial impacts on returning adults.

Interactive Effects of Water Diversion and Climate Change for Juvenile Chinook Salmon in the Lemhi River Basin (U.S.A.)

“…The climate variables that best explained juvenile survival were spring streamflow and summer temperature; higher streamflow and lower temperature increased survival. This effect of spring streamflow on juvenile survival is consistent with results of an earlier study on the Lemhi Basin (Arthaud et al ) and suggests it is important to maintain sufficient streamflow during the low‐flow period between the start of irrigation season and the snowmelt runoff peak. Although spring streamflow and summer temperature were clearly important there was considerable unexplained variation, which suggests there are also important nonclimate factors (e.g., resource availability) driving juvenile survival.…”

Climate variables explain neutral and adaptive variation within salmonid metapopulations: the importance of replication in landscape genetics

“…disperse) to streams with colder temperatures when their natal streams are prohibitively warm during migration events (Bradford et al 2009), which has been observed in Chinook salmon (O. tshawytscha) populations across the CRB (Westley et al 2015). Streams with decreased flow might further increase genetic differentiation through stranding of migrating steelhead, decreasing rearing habitat and increasing juvenile mortality (May & Lee 2004;Harvey et al 2006;Arthaud et al 2010).…”

Competitive release modifies the impacts of hydrologic alteration for a partially migratory stream predator

“…Additionally, trophic interactions that propagate to upper trophic levels have been shown to be mediated by annual and subannual variations in flow (Power et al 2008;Kurle & Cardinale 2011). As such, these populations can provide an informative model organism for studying the effect of environmental change and the complex impacts to upper trophic levels when community structure and function is anthropogenically altered (Arthaud et al 2010). Impacts on juveniles during their freshwater existence are often experienced directly through a change in food supply or an increase in temperatures (Connor & Pflug 2004;Richter & Kolmes 2005) or more subtly as a change in trophic structure (Power et al 1995).…”

“…For migratory populations, altered flow conditions in freshwater can have direct impacts on the demographics of rearing life history stages, ultimately impacting viability of the returning adult population (Arthaud et al 2010). For instance, increased temperatures and other impacts to energetic costs (e.g., active metabolism, prey availability) can impact growth rate and survival of juvenile salmonids (Jager et al 1997;Nislow et al 2004;Piccolo et al 2008).…”