The U.S. Global Ocean Ecosystem Dynamics (GLOBEC) North East Pacific (NEP) program funded MSI to participate in a coho salmon (Oncorhynchus kisutch) synthesis project entitled “Environmental Influences on Growth and Survival of Southeast Alaska Coho Salmon in Contrast with other Northeast Pacific Regions”. The goal was to improve predictability of living marine resources of the region by increasing understanding of ecosystem interactions and the coupling between the physical environment and living resources. The research examines how ocean conditions affect Pacific salmon populations by understanding the mechanisms underlying the processes that influence survival of salmon cohorts in the NEP. Salmon are key species for this research effort because of the linkage of regional abundance of salmon stocks to climate shifts in the NEP.

Average growth rate of juvenile coho salmon from strait habitats.

Coho salmon have been studied in both Southeast Alaska (SEAK) and in the California Current System (CCS) and were found to co-vary inversely, suggesting that region-wide factors have different effects on salmon in these two systems. As a result, GLOBEC placed a major emphasis on synthesis research between locations and over time for the NEP. MSI has been monitoring juvenile salmonids in the coastal straits of SEAK for over ten years. Southeast Coastal Monitoring (SECM) ecosystem surveys provides an excellent source of long term data for this effort. Central to the project was analysis of biophysical conditions of coho habitat while looking for abundance indices and correlations. The coho synthesis project includes research partners from other institutions including University of California at Davis, Oregon State University, NOAA Pacific Marine Environmental Laboratory (PMEL), University of Washington, and the University of Alaska Fairbanks, School of Fisheries and Ocean Science, Juneau Center.

Juvenile coho salmon from Icy Strait in Southeast Alaska are measured for length.

The growth rate and condition of juvenile coho salmon was calculated using SECM data to examine the hypothesis that survival of coho salmon is determined by availability and spatial arrangement of high quality habitat. These two parameters were then synthesized with associated biophysical environment parameters in northern SEAK to better understand both juvenile coho abundances and their habitat characterization.

Which habitat variables best predict coho abundance during summer months?

June: Salinity explains 19% of the variation in coho catch per unit effort (CPUE) in trawls. Temperature and zooplankton also have significant correlations with coho CPUE.

July: Temperature explains 9% of the variation in coho CPUE. Chlorophyll, salinity, and year also have significant correlations with coho CPUE.

August: Habitat variables did not explain any of the variation in coho CPUE. However, the parameter "year" explains 15% of the variation in coho CPUE. This suggests that recruitment differences each year may outweigh habitat influences on coho CPUE.

Are fish above or below the average? Mean condition residuals (CR) from length to weight regressions of juvenile coho salmon from strait habitats.

To address habitat influence, data on zooplankton, temperature, salinity, mixed layer depth, and surface chlorophyll were examined. Correlation analysis and regression techniques were used to predict which parameters best explain the variation in coho CPUE. These analyses found that habitat variables explain only 19% of the variation in coho CPUE.

Although juvenile coho CPUE shows no relationship with adult coho harvest, year-class strength of both pink (O. gorbuscha) and coho salmon is positively associated with the abundance of juvenile pink salmon in the prior year. Juvenile coho CPUE may not predict adult coho harvest because it could be a measure of habitat preference that affects migration timing to the Gulf of Alaska (GOA), rather than an index of annual recruitment. Significant additional and variable mortality may occur in the GOA after juvenile coho have left Southeast Alaskan waters.

This research will be published in a special GLOBEC issue of Deep Sea Research in the paper "A Top-down Survival Mechanism During Early Marine Residency Explains Coho Salmon Year-class Strength in Southeast Alaska".

Contact:
Jacob LaCroix
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801
(907) 789-6088
Jacob.LaCroix@noaa.gov