Potential for ecological nonlinearities and thresholds to inform Pacific salmon management

Abstract

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds—incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncorhynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve salmon outcomes. It appears that nonlinear dynamics are not uncommon in salmon ecology and that many management arenas may potentially leverage them to enable more effective or efficient decisions. Indeed, decisions guided by nonlinearities and thresholds may be particularly desirable considering salmon management arenas are often characterized by limited resources and mounting ecological stressors, practical constraints, and conservation challenges. More broadly, many salmon systems are data‐rich and there are an extensive range of ecological contexts in which salmon are sensitive to anthropogenic decisions. Approaches developed to leverage nonlinearities in salmon ecology may serve as examples that may inform analogous approaches in other systems and taxa.

Nonlinear survival of imperiled fish informs managed flows in a highly modified river

“…Therefore, it is important to explore possible nonlinearities between environmental resources and ecosystem processes, with the particular objective of finding information that is more actionable to resource managers. This is especially pertinent to Pacific salmon stocks that are often found in the middle of constrained resource management arenas (Munsch et al 2020).…”

Density Dependence in Three Snake River Sockeye Salmon Nursery Lakes in Central Idaho

“…Pacific salmon Oncorhynchus spp. experience nonlinear and threshold dynamics (Munsch et al 2020). In the Sawtooth Valley lakes, we identified a zooplankton-growth threshold useful for guiding stocking and lake fertilization activities.…”

Prioritizing actions: spatial action maps for conservation

“…Conservation actions also take place in the context of complex land and seascapes where many individuals (human and other species) are interacting across space and through time; and while these complex interactions are often difficult to realistically account for, they are essential to strive to better understand as they can lead to nonlinearities in impact, probability of success, and conservation costs. 148 , 149 As previously mentioned, approaches for addressing interactions in spatial action mapping should be more regularly employed, whether through simple (e.g., enlarging planning units to reduce influence of small‐scale interactions), moderate (e.g., running multiple plan scenarios to reveal influence of interactions on plan outcomes), or more complex (e.g., building complex dependencies into models that estimate impacts) approaches. Additional advances are needed to allow consideration of changes in conditions, likely outcomes, and the relevance or social value of such outcomes over time.…”