GLOBEC: Growth and Survival of Juvenile Salmon

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RauSalmon populations in the California Current System (CCS), and coho salmon in particular, have been in severe decline since the 1980s, coinciding with the 1977 regime shift, and in contrast to record productivity in the Gulf of Alaska. The specific linkages between oceanographic changes and salmon survival in the marine.enviromnent are not well understood. GLOBEC has chosen to compare two regions of the Northern California Current divided by Cape Blanco, Oregon (43 degrees N) where an "upwelling jet" moves off the shelf. The regions north and south of Cape Blanco differ in intensity and stability of upwelling, temperature, and offshore transport. Evidence indicates that due to the physical conditions, the distribution and production of biota may differ north and south of Cape Blanco, providing the opportunity to compare and contrast the relationship between specific oceanographic processes and biological productivity. The investigators will use process oriented studies to examine mechanistic linkages between the physical and biological processes that are associated with habitat quality critical to recruitment of juvenile salmon. Juvenile coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon will be collected along transects between Eureka, CA to Newport, OR during May/June and September of 2000 and 2002. Sampling efforts will coincide with mesoscale and fine-scale surveys of physical (e.g., location of eddies, fronts, upwelling, offshore transport import; mixed layer depth, sea surface temperature, mixed layer depth) and biological (areas and density of primary and secondary productivity) features within the same regions conducted by other GLOBEC researchers. The salmon investigators will measure the growth rate, size variability, bioenergetic condition, pathogen prevalence and intensity in juvenile salmon as conditions of survival. By correlating indices in the Northern CCS with the trophic relationship studies, they will test the hypotheses that oceanographic features leading to high productivity of lower trophic levels translates to higher growth rates, condition and greater salmon recruitment through "bottom-up" forces. Also, the degree of correlation between these indices and variations in isotope natural abundances (14C, 13C, 15N) in juvenile salmon will be used to directly test the hypothesis that diet specificity and vertical ocean advection affect juvenile salmon health and condition. The investigators also will compare juvenile coho and chinook slamon growth and condition from different regions of the Northeast Pacific (e.g., Alaska, British Columbia, Washington and northern Oregon) and to the historical record (prior to the last regime shift) where available and applicable. These results will provide information on the relationships between ocean variability and juvenile salmon survival on temporal (interdecadal) and spatial (basin-wide, mesoscale, and local) scales.