Population diversity and the portfolio effect in fisheries Daniel Schindler
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Transcript of Population diversity and the portfolio effect in fisheries Daniel Schindler
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Population diversity and the portfolio effect in fisheries
Daniel Schindler
Keeler Professor of Aquatic and Fishery Sciences
University of Washington
Seattle, WA 98195
Thanks to:
National Science Foundation, Gordon and Betty Moore Foundation, Alaska Salmon processors
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Biological diversity is important for ecosystem stability…
…but does this apply to individual species?
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North Pacific Ocean
Bristol Bay
Wood RiverL.A. Rogers
each withmany
populations
9 major rivers
Salmon habitat in Bristol Bay
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Commercial fisheries for sockeye salmon in Bristol Bay have been sustained for over 120 years
- record catches have occurred within the last 20 years -
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Togiak
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data from ADFG
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Number of sockeye salmon caught in Bristol Bay (1893-2010)
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Bristol Bay river stocks
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Different dynamics in stocks of Bristol Bay sockeye produce portfolio effects in fisheries
Sockeye salmon returns to Bristol Bay rivers
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Age diversity
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Salmon returns to Bristol Bay are two times more reliable than the individual
components of the portfolio
Eroded portfolio
2.2 times more variable than the
Bristol Bay salmon portfolio
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The front line at Egegikhttp://www.absc.usgs.gov/research/Fisheries/Lake_Clark/subsistence.htm
How does reliability affect people dependent on fisheries?
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Fisheries are closed 40 times every century
Bristol Bay (intact portfolio)
Bristol Bay (eroded portfolio)
minimum spawners
average
Variability in salmon increases the rate of fisheries closures
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Time (100 years)
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L.A. Rogers
Lake beaches
Small streams
Sockeye salmon have different biological features, depending on the habitat they occupy
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Habitat conditions vary among locations in watersheds
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August 2000, NASA
Salmon habitat is also different among locations in the ocean
Locations where juvenile salmon enter the ocean
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NOAA
Portfolio effects derive from intact and viable habitat
Bristol Bay, Alaska Pacific Northwest
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* Conservation and management should recognize the value of diversity within individual species, and the habitat conditions that produce this diversity
* Maintaining genetic diversity and viable habitat is one way to build insurance for climate change. The weak stock today may be the strong one tomorrow!
* Climate change, ocean acidification, etc. make the future far more uncertain than usual, the portfolio concept is one way to build insurance for the future
(How are you spreading your risk? Among species? Among stocks?)
* Specific strategies will be ecosystem-specific, but do not necessarily require finer scale management.
Bristol Bay