Complex ecological processes determine whether and how fish species survive in the ocean. For some fishes such as the Pacific salmon, these processes are thoroughly studied and modeled. For eulachon (Thaleichthys pacificus), however, these processes are more mysterious despite their trophic link to salmon and similar anadromous life history. The ocean ecology of eulachon has been identified by NOAA as a key knowledge gap and research priority for the declining species, which is listed under the Endangered Species Act as “threatened” on the west coast of the U.S. Declines in abundance are a problem because eulachon are a culturally and historically important species for Native American and First Nations people and a critical component of freshwater, estuarine, and marine food webs.
The marine ecology of eulachon may be relatively understudied, but data collected and compiled for salmon can partially fill this gap. NOAA has developed ocean ecosystem indicators (physical, chemical, and biological factors) that are used to predict salmon returns. I applied these indicators to a new question using multivariate analyses: are the indicators used for salmon also predictive for a trophically related and ecologically similar species? And what environmental and biological factors in the ocean drive fluctuations in eulachon abundance in a major spawning basin?
Ocean ecosystem indicators in years of ocean residency are correlated with eulachon abundance in the Columbia River. Indicators related to large-scale and bottom-up factors such as the status of the Pacific Decadal Oscillation and prey abundance better describe eulachon abundance compared to local and top-down factors. The ocean ecosystem indicators developed for salmon are a reasonable starting point to model eulachon abundance in the Columbia River and for the Southern Distinct Population Segment.