Weakened portfolio effect in a collapsed salmon population complex

Author:

Carlson Stephanie Marie1,Satterthwaite William Hallowell23

Affiliation:

1. University of California, Department of Environmental Science, Policy, and Management, 130 Mulford Hall #3114, Berkeley, CA 94720, USA.

2. University of California, Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, Santa Cruz, CA 95064, USA.

3. MRAG Americas, P.O. Box 1490, Capitola, CA 95010, USA.

Abstract

Recent research has highlighted the importance of interpopulation diversity in fostering the stability of population complexes. Here we focus on California’s recently collapsed fall-run Chinook salmon ( Oncorhynchus tshawytscha ) and ask whether portfolio effect induced buffering is observed across the complexity hierarchy from individual populations to populations within a river basin (Sacramento, San Joaquin) to the entire Central Valley. Some buffering was observed when comparing the coefficient of variation in adult returns to a given river basin with its constituent populations but not when comparing returns to the entire Central Valley with its constituent basins because of disproportionately many fish returning to the Sacramento Basin. Moreover, we report that positive correlations in population dynamics between rivers were stronger in the last 25 years of the study compared with the first 25 years. Together, these results suggest evidence of only a weak portfolio effect that has deteriorated in recent years. Nonetheless, we also report that correlations between rivers decreased significantly with distance, suggesting that some biocomplexity remains. Our results suggest that the greatest potential for strengthening the portfolio effect would come through restoration of San Joaquin Basin populations, which at low abundance currently contribute little to the overall buffering capacity despite low cross-basin correlations.

Publisher

Canadian Science Publishing

Subject

Aquatic Science,Ecology, Evolution, Behavior and Systematics

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