One hundred‐seventy years of stressors erode salmon fishery climate resilience in California’s warming landscape

Abstract

People seek reliable natural resources despite climate change. Diverse habitats and biologies stabilize productivity against disturbances like climate, prompting arguments to promote climate-resilient resources by prioritizing complex, less-modified ecosystems. These arguments hinge on the hypothesis that simplifying and degrading ecosystems will reduce resources' climate resilience, a process liable to be cryptically evolving across landscapes and human generations, but rarely documented. Here, we examined the industrial era (post 1848) of California's Central Valley, chronicling the decline of a diversified, functional portfolio of salmon habitats and life histories and investigating for empirical evidence of lost climate resilience in its fishery. Present perspectives indicate that California's dynamic, warming climate overlaid onto its truncated, degraded habitat mosaic severely constrains its salmon fishery. We indeed found substantial climate constraints on today's fishery, but this reflected a shifted ecological baseline. During the early stages of a stressor legacy that transformed the landscape and --often consequently --compressed salmon life history expression, the fishery diffused impacts of dry years across a greater number of fishing years and depended less on cool spring-summer transitions. The latter are important given today's salmon habitats, salmon life histories, and resource management practices, but are vanishing with climate change while year-to-year variation in fishery performance is rising. These findings give empirical weight to the idea that human legacies influence ecosystems' climate resilience across landscapes and boundaries (e.g., land/ sea). They also raise the question of whether some contemporary climate effects are recent and attributable not only to increasing climate stress, but to past and present human actions that erode resilience. In general, it is thus worth considering that management approaches that prioritize complex, less-modified ecosystems may stabilize productivity despite increasing climate stress and such protective actions may be required for some ecological services to persist into uncertain climate futures.

A meta‐analysis and model comparison of juvenile salmon growth across different habitat types

“…In California's Central Valley, Chinook salmon have faced a series of anthropogenic threats, including gold mining, industrial fishing, dam construction, and climate change (Munsch, Greene, Mantua, & Satterthwaite, 2022). These and other pressures have led to a decline in populations (Yoshiyama, Fisher, & Moyle, 1998) and caused the National Oceanic and Atmospheric Administration (NOAA) to list two of the four central valley populations of Chinook salmon as either endangered or threatened (NOAA, 2005).…”

Identifying a pathway towards recovery for depleted wild Pacific salmon populations in a large watershed under multiple stressors

“…This context helped to identify strategies to mitigate the expected effects of climate change, for example, intensive restoration of lost and degraded rearing and spawning habitat was predicted to provide substantial conservation benefit to Fraser River salmon populations. This strategy can facilitate enhanced capacity for salmon to withstand stochastic climate events and adapt to future change (Atlas et al, 2021; Gayeski et al, 2018; Munsch et al, 2022).…”

Rediscovering, reevaluating, and restoring Entiatqua: Identifying pre‐Anthropocene valleys in North Cascadia, USA

“…"Entiatqua" translates literally as "place of grassy water", suggesting that, in the past, vegetated, RWCs were the defining feature of the river valley (Bright, 2004, Jeremy FiveCrows, personal communication, January 20th, 2022. Nodine, Beechie, & Zabel, 2019;Cordoleani, Holmes, Bell-Tilcock, Johnson, & Jeffres, 2022;Jeffres, Holmes, Sommer, & Katz, 2020;Munsch, Greene, Mantua, & Satterthwaite, 2022).…”

“…Complex and well‐connected rivers (at all discharge levels) and wetland habitats extending across a valley floor have been shown to be highly productive and would have served as a foundation of the basin's capacity to support salmon and other aquatic biota (Bond, Nodine, Beechie, & Zabel, 2019; Cordoleani, Holmes, Bell‐Tilcock, Johnson, & Jeffres, 2022; Jeffres, Holmes, Sommer, & Katz, 2020; Munsch, Greene, Mantua, & Satterthwaite, 2022).…”