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Assessment of ultraviolet radiation exposure during freshwater rearing on early marine mortality in migrating juvenile sockeye and coho salmon Many salmon populations in B.C. have declined over the last couple decades, largely as a result of decreased marine survival rates that do not include fishing. Causes for the declines in marine survival rates are not well understood. Before these causes can be properly addressed, we need to better understand the patterns of mortality- where and when mortality predominantly occurs during the first few weeks or months of ocean life. This project, currently ongoing, will involve tagging juvenile salmon smolts from two hatcheries (Tenderfoot Creek Hatchery, Tenderfoot coho; Inch Creek Hatchery, Cultus Lake sockeye) with coded acoustic transmitters and tracking the migrations of individual fish downstream and during their early ocean life. Downstream and early ocean survival rates will be estimated for these populations. The fish that will be tagged were placed under experimental treatment beginning in summer 2006 to address the hypothesis that ultraviolet-B exposure from sunlight during freshwater rearing has detrimental survival consequences that are not observed until after ocean entry. Fish from UV-shaded tanks and from UV-exposed tanks (the controls) will both be tagged, and their early ocean survival rates will be compared. This study will extend the short time series of migration and mortality patterns already established for these populations from studies in 2004-2006 and improve our ability to determine the factors responsible for that variation in survival. This project will also demonstrate that experiments can be conducted addressing questions related to the ocean life of salmon using the Pacific Ocean Shelf Tracking Project’s monitoring array of acoustic receivers. Cultus Lake sockeye smolts will be tagged in early April and released in early to mid-April, while Tenderfoot Creek coho smolts will be tagged and released in early May. Once the final results have been assessed, they will be reported. (Project 07D1) Final Results Little difference was found between UVB-exposed and non UVB-exposed groups in survival. The POST project was very successful in quantifying migration patterns and estimating early ocean mortality rates for many salmonid populations. This allowed for the comparison of survival rates between population from different areas, between hatchery- reared and wild populations, and between species. The tool can also allow experiments to be conducted on juvenile salmon in the marine environment. Through sufficient tagging programs, various factors on survival rates or migration rates could be experimentally evaluated within population.
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