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Application of Portfolio Theory in Recovery Planning for Pacific Salmon.
Sloat, M., Joe Ebersole, M. Snyder, AND J. Armstrong. Application of Portfolio Theory in Recovery Planning for Pacific Salmon. Oregon Chapter American Fisheries Society, Eugene, OR, March 13 - 16, 2018.
Portfolio theory is a framework used to optimize return based on a given level of risk. By assembling portfolios of stocks with a diverse set of responses to market fluctuations, investors can reduce overall risk. This framework has been applied to Pacific salmon fisheries to show how diverse populations, with different response trajectories, contribute to overall population stability. Portfolio theory also has the potential to aid in recovery planning for threatened and endangered Pacific salmon but it has not been applied in this context. To explore the utility of this concept to recovery planning, we are examining long-term population trends in Oregon Coastal Coho salmon. Populations are occasionally highly synchronous coast-wide, suggesting similar responses to climate fluctuations, hatchery production, or other large scale dynamics. But the magnitude of fluctuations can be highly variable, likely reflecting differences in watershed habitat characteristics, water quality, or population attributes. The most stable populations are associated with coastal lakes where juvenile salmon can escape some of the winter habitat limitations they would otherwise face in coastal streams. We are continuing to investigate watershed attributes that may be associated with salmon population resilience. The purpose of this presentation is to share our efforts and results to date with the interagency coho salmon recovery workgroup, states, and tribes to solicit feedback and help direct future products to be of best use for recovery planning, water quality protection, and watershed management. This Abstract contributes to SSWR 3.01C.
Ecological applications of portfolio theory demonstrate the utility of this analytical framework for understanding the stability of commercial and indigenous Pacific Salmon fisheries. Portfolio theory also has the potential to aid in recovery planning for threatened and endangered Pacific salmon but it has not been applied in this context. This study applies portfolio theory to recovery planning for the Oregon Coastal Coho Salmon (Oncorhynchus kisutch) Evolutionary Significant Unit (ESU). This ESU includes 21 independent populations organized into five geographically and genetically cohesive strata. Federal recovery goals aim to stabilize a minimum of 50 percent of independent populations within each stratum. We apply portfolio theory to time series of spawner abundance to identify stability properties of populations within and among ESU strata. We also correlate population stability properties with watershed-scale habitat features to explore landscape controls on coho salmon population dynamics. Our work identified high variation among five ESU strata in the temporal stability of coho salmon populations. Variation among strata was associated with watershed-scale habitat features. In particular, the stratum with highest levels of temporal population stability (lowest coefficient of variation [CV] in population abundance) is notable for the presence of coastal lakes that are known to relax winter habitat survival bottlenecks for juvenile coho salmon. We observed low temporal coherence in population abundance within other strata, suggesting considerable response diversity of populations in close proximity. These results reflect an important analytical framework for designing conservation strategies for population aggregations such as Pacific Salmon ESUs.