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Myths: Salmon and the Sea

Myths: Salmon and the Sea. Limiting factors are all in fresh water, hence marine survival does not vary The ocean has unlimited capacity to support salmon All juveniles salmonids migrate rapidly to the north. OSU purse seining—1979-1985. Ocean carrying capacity. It varies

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Myths: Salmon and the Sea

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  1. Myths: Salmon and the Sea • Limiting factors are all in fresh water, hence marine survival does not vary • The ocean has unlimited capacity to support salmon • All juveniles salmonids migrate rapidly to the north

  2. OSU purse seining—1979-1985

  3. Ocean carrying capacity • It varies • Seasonally—Coastal Upwelling • Interannually—El Niño/La Niña • Interdecadally—Pacific Decadal Oscillation • Intercentenially

  4. 1983 El Niño

  5. Predictions for 1983 coho returns: 1.3 million vs. 600 thousand

  6. Timing (spring transition) and intensity are both important Drifter tracks temperature Chlorophyll

  7. Strong upwelling=good survival during cool PDO • Poor correlation with • upwelling during warm • PDO • Strong stratification

  8. Pacific Decadal Oscillation. Cool or negative phase Warm or positive phase

  9. OPI (hatchery) coho marine survival: PDO and stratification Why? Leading hypothesis: changes in ocean conditions impact the entire marine food-web 1976-77 PDO shift Strong stratification in 1990s

  10. upwelling food webs in our coastal ocean Cool water, weak stratification high nutrients, a productive “subarctic” food-chain with abundant forage fish and few warm water predators Warm stratified ocean, few nutrients, low productivity “subtropical” food web, a lack of forage fish and abundant predators

  11. What controls survival?Hypotheses and mechanisms • Critical period during early ocean life is affected by ocean conditions • Ocean productivity, prey availability and growth • Faster growth, less predation • Critical size to avoid winter starvation • Area and distribution of highly productive water • Predation intensity—more big predators when warm waters intrude and close to shore

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