A synthesis of the coast‐wide decline in survival of West Coast Chinook Salmon (<i>Oncorhynchus tshawytscha,</i>Salmonidae)

Welch, David W.; Porter, Aswea D.; Rechisky, Erin L.

doi:10.1111/faf.12514

Cited by 51 publications

(34 citation statements)

References 75 publications

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“…Downward trends in smolt‐to‐adult return rates of Chinook salmon populations along the northeastern Pacific Ocean support a conclusion of strong effects from the ocean (Welch et al. 2021); however, freshwater carryover effects are not altogether negligible. Studies limited by the mechanisms examined and the samples assumed to represent a whole population could lead to an incomplete understanding of carryover effects.…”

Section: Discussionmentioning

confidence: 60%

“…Even though marine covariates such as the Pacific Decadal Oscillation and NPGO indices generally have stronger associations with ocean survival and recruitment than freshwater covariates Schaller 2010, Kilduff et al 2015), our study found that the river system can have considerable influence on ocean survival. Downward trends in smolt-to-adult return rates of Chinook salmon populations along the northeastern Pacific Ocean support a conclusion of strong effects from the ocean (Welch et al 2021); however, freshwater carryover effects are not altogether negligible. Studies limited by the mechanisms examined and the samples assumed to represent a whole population could lead to an incomplete understanding of carryover effects.…”

Section: Discussionmentioning

confidence: 66%

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Role of carryover effects in conservation of wild Pacific salmon migrating regulated rivers

et al. 2021

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Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark-recapture model to~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species.

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Section: Discussionmentioning

confidence: 60%

Section: Discussionmentioning

confidence: 66%

Role of carryover effects in conservation of wild Pacific salmon migrating regulated rivers

et al. 2021

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“…These regime shifts alter fishery quotas and recovery timelines and are associated with the widespread decline of wild Pacific salmonids across the Pacific Northwest (Dorner et al, 2013;Peterman & Dorner, 2012;Teresa A'Mar et al, 2009). Despite marine regime shifts having been frequently observed in Pacific salmonids (Welch et al, 2020), descriptions of freshwater regimes shifts are rare (but see Atlas et al, 2015;Jones et al, 2020;Scheuerell et al, 2020), and relatively few studies have assessed regime shifts in both marine and freshwater contexts. Moreover, studies generally focus on a single species even though salmon rivers often support diverse communities.…”

Section: Introductionmentioning

confidence: 99%

Marine and freshwater regime changes impact a community of migratory Pacific salmonids in decline

Wilson

Bailey

Davies

et al. 2021

Global Change Biology

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Marine and freshwater ecosystems are increasingly at risk of large and cascading changes from multiple human activities (termed "regime shifts"), which can impact population productivity, resilience, and ecosystem structure. Pacific salmon exhibit persistent and large fluctuations in their population dynamics driven by combinations of intrinsic (e.g., density dependence) and extrinsic factors (e.g., ecosystem changes, species interactions). In recent years, many Pacific salmon have declined due to regime shifts but clear understanding of the processes driving these changes remains elusive. Here, we unpacked the role of density dependence, ecosystem trends, and stochasticity on productivity regimes for a community of five anadromous Pacific salmonids (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden, and Coastal Cutthroat Trout) across a rich 40-year time-series. We used a Bayesian multivariate state-space model to examine whether productivity shifts had similarly occurred across the community and explored marine or freshwater changes associated with those shifts. Overall, we identified three productivity regimes: an early regime (1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990), a compensatory regime (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009), and a declining regime (since 2010) where large declines were observed for Steelhead, Dolly Varden, and Cutthroat Trout, intermediate declines in Coho and no change in Pink Salmon. These regime changes were associated with multiple cumulative effects across the salmon life cycle. For example, increased seal densities and ocean competition were associated with lower adult marine survival in Steelhead. Watershed logging also intensified over the past 40 years and was associated with (all else equal) ≥97% declines in freshwater productivity for Steelhead, Cutthroat, and Coho. For Steelhead, marine and freshwater dynamics played approximately equal roles in explaining trends in total productivity. Collectively, these changing environments limited juvenile production and lowered future adult returns. These results reveal how changes in freshwater and marine environments can jointly shape population dynamics among ecological communities, like Pacific salmon, with cascading consequences to their resilience.

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“…We provided evidence that the success of river migration by smolts in the River Endrick was low with only 36% of tagged smolts exiting the mouth of the river. This seems to be a trend emerging across rivers in Scotland (Adams, Unpublished data; Honkanen et al 2021, Lothian et al 2018) but also elsewhere (Flávio, et al 2020a, Flávio et al 2020b, Gibson et al 2015) and other salmonid species (Welch et al 2021, Wilson et al 2021. Undeniably, the process of smolting is a critical phase in the life-cycle of anadromous salmonids and has been associated with substantial mortality rates (Clark et al 2016, Halfyard, et al 2012, Thorstad et al 2012.…”

Section: Discussionmentioning

confidence: 95%

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

Chavarie

Honkanen

Newton

et al. 2021

Preprint

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The process of smolting is a critical phase in the life-cycle of anadromous salmonids and it has been associated with substantial rates of mortality. Survival during freshwater and marine migration is known to have population level effects, thus an understanding of the patterns of mortality has the potential to yield important insights into population bottlenecks. Despite important advancements in tracking techniques, the specifics of mortality events in anadromous salmonids during their initial migration to sea remains somewhat elusive. Here, we develop a framework combining spatial and temporal detections of smolt riverine migration from two tracking techniques, which enable inferences to be made about mortality locations, causes, and rates. We embed this framework into a fine-scale behaviour study of migration and social structure. In this study, we demonstrate that during their initial riverine transitional phase, smolts were particularly vulnerable to predators. Specifically, avian predation appeared to be the main cause of mortality (42%), although piscine predation events were not trivial (14%). Our results suggested some direct and indirect tagging-induced mortality (e.g., through increased predation vulnerability), which highlights the importance of determining tagging mortality in a telemetry study to ensure adequate interpretation of migration success. There is evidence that predation induced selection on smolt morphology. Unsuccessful river salmon migrants with a phenotype comprising a shorter head and jaw and smaller eye had a higher probability of mortality in the later parts of riverine migration where avian and aquatic predation mortality dominated. In contrast, mortality earlier in river migration was independent of phenotype, most likely a result of tagging effects. Successfully river migrants were found to be interacting with each other, often in a pair or as a trio, indicating that a few individuals of Atlantic salmon and sea trout formed notable intra- and interspecific social associations. However, the heterogeneity of the social associations of successful migrants did not support the assumption that social network features attributed any clear specific benefits of reduced predation risk. Overall, by estimating migration loss and its variability, our study framework should help to guide management actions to mitigate the widespread population declines these species are currently facing.

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A synthesis of the coast‐wide decline in survival of West Coast Chinook Salmon (Oncorhynchus tshawytscha,Salmonidae)

Cited by 51 publications

References 75 publications

Role of carryover effects in conservation of wild Pacific salmon migrating regulated rivers

Role of carryover effects in conservation of wild Pacific salmon migrating regulated rivers

Marine and freshwater regime changes impact a community of migratory Pacific salmonids in decline

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

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