myths: salmon and the sea
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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 - PowerPoint PPT PresentationTRANSCRIPT
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 OSU Purse Seining (1981(1981--1985)1985)OSU purse seining—1979-1985
Ocean carrying capacity
• It varies– Seasonally—Coastal Upwelling– Interannually—El Niño/La Niña– Interdecadally—Pacific Decadal Oscillation– Intercentenially
1983 El Niño
Predictions for 1983 coho returns: 1.3 million vs. 600 thousand
Timing (spring transition) and intensity are both important
Drifter tracks temperature Chlorophyll
• Strong upwelling=good survival during cool PDO
•Poor correlation with upwelling during warm PDO
•Strong stratification
Pacific Decadal Oscillation.
Warm or positive phase Cool or negative phase
OPI (hatchery) coho marine survival: PDO and stratification
0
0.02
0.04
0.06
0.08
0.1
0.12
0.1419
70
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
Return Year
Surv
ival
Why? Leading hypothesis: changes in ocean conditions impact the entire marine food-web
1976-77 PDO shift
Strong stratification in 1990s
upwelling food webs in our coastal ocean
Cool water, weak stratificationhigh nutrients, a productive “subarcticsubarctic” food-chain with abundant forage fish and few warm water predators
Warm stratified ocean, fewnutrients, low productivity “subtropicalsubtropical” food web, a lack of forage fish and abundant predators
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