Response of ecosystem metabolism to low densities of spawning Chinook salmon

Freshwater Science
By: , and 



Marine derived nutrients delivered by large runs of returning salmon are thought to subsidize the in situ food resources that support juvenile salmon. In the Pacific Northwest, USA, salmon have declined to <10% of their historical abundance, with subsequent declines of marine derived nutrients once provided by large salmon runs. We explored whether low densities (<0.001 spawners/m2) of naturally spawning Chinook Salmon (Oncorhynchus tshawytscha) can affect ecosystem metabolism. We measured gross primary production (GPP) and ecosystem respiration (ER) continuously before, during, and after salmon spawning. We compared downstream reaches with low densities of spawning salmon to upstream reaches with fewer or no spawners in 3 mid-sized (4th-order) rivers in northern Washington. In addition, we measured chemical, physical, and biological factors that may be important in controlling rates of GPP and ER. We observed that low densities of spawning salmon can increase GPP by 46% during spawning, but values quickly return to those observed before spawning. No difference in ER was observed between up- and downstream reaches. Based on our results, salmon density, temperature, and the proximity to salmon redds were the most important factors controlling rates of GPP, whereas temperature was most important for ER. These results suggest that even at low spawning densities, salmon can stimulate basal resources that may propagate up the food web. Understanding how recipient ecosystems respond to low levels of marine derived nutrients may inform nutrient augmentation studies aimed at enhancing fish populations.

Publication type Article
Publication Subtype Journal Article
Title Response of ecosystem metabolism to low densities of spawning Chinook salmon
Series title Freshwater Science
DOI 10.1086/686686
Volume 35
Issue 3
Year Published 2016
Language English
Publisher University of Chicago Press
Publisher location Chicago, IL
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description 17 p.
First page 1874
Last page 1890
Online Only (Y/N) N
Additional Online Files (Y/N) N
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