Effects of Climate on Variability of Coho Salmon Populations
Current Status of Accomplishment or Milestone: Research at PFEL was recently highlighted in publication of the manuscript "Climate Variability and Marine Survival of Coho Salmon (Oncorhynchus kisutch) in the Oregon Production Area" in the journal Fisheries Oceanography.
Background: Recent years have seen a decline in salmon abundance from the Strait of Georgia to California, whereas Alaskan salmon runs have been generally at their highest historical levels. Native stocks of coho salmon in the southern part of its range have displayed a particularly worrisome trend, having disappeared from approximately half the streams that historically contained this species; abundance is presently estimated to be less than 6% that in 1940. Coho salmon are presently listed as threatened in California and part of Oregon.
Purpose of Activity/Goal of Project: The purpose of the work was to evaluate the influence of ocean variability and climate on the survival of coho salmon populations.
Description of Accomplishment and Significant Results: Time series for natural runs of coho salmon from the Oregon coastal region (1970-94) and marine survival of hatchery-reared coho salmon in the Oregon Production Index area (1960-94) was shown to be related to a suite of meteorological and oceanographic variables, including strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity in the region. Multiple regression analysis indicated that coho marine survival is significantly and independently related to these conditions in northern and southern sectors of this region during both the periods of smolt outmigration and the second year at sea. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): Understanding the role of natural environmental variability on salmon populations will be crucial to recovery goals. Ocean survival has been shown to be highly variable on regime scales. The new information provided by this work will help translate the signals inherent in ocean variability into the biological response for this species.
Problems: None
Key Contact: Franklin B. Schwing, (831-648-9034, Franklin.Schwing@noaa.gov)