Population diversity and the portfolio effect in fisheries

Daniel Schindler

Keeler Professor of Aquatic and Fishery Sciences

University of Washington

Seattle, WA 98195

deschind@u.washington.edu

Thanks to:

National Science Foundation, Gordon and Betty Moore Foundation, Alaska Salmon processors

Biological diversity is important for ecosystem stability…

…but does this apply to individual species?

North Pacific Ocean

Bristol Bay

Wood RiverL.A. Rogers

each withmany

populations

9 major rivers

Salmon habitat in Bristol Bay

Commercial fisheries for sockeye salmon in Bristol Bay have been sustained for over 120 years

- record catches have occurred within the last 20 years -

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

45,000,000

50,000,000

1893

1903

1913

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1943

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1973

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1993

2003

Year

Co

mm

erc

ial

ca

tch

Togiak

Ugashik

Egegik

Nushagak

Naknek-Kvichak

data from ADFG

Com

mer

cial

cat

ch

Number of sockeye salmon caught in Bristol Bay (1893-2010)

Bristol Bay river stocks

0.01

0.1

1

10

1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006

Year

Rel

ativ

e ru

n si

ze

Rel

ativ

e ru

n si

ze

Different dynamics in stocks of Bristol Bay sockeye produce portfolio effects in fisheries

Sockeye salmon returns to Bristol Bay rivers

0.01

0.1

1

10

1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006

Year

Rel

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e ru

n si

ze

1

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3

Age diversity

0.01

0.1

1

10

1

Major rivers

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0.1

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10

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Streams

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0.1

1

10

1

All the same age

0.01

0.1

1

10

1

year

Tot

al r

etur

n (r

elat

ive)

Bristol Bay

1960 2010

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

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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100 Fisheries are closed 4 years every century

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

X X X X

XXXXXXXXXXXXXXXXXXXXXXXXXXXX X X

Time (100 years)

Num

ber

of r

etur

ning

sal

mon

L.A. Rogers

Lake beaches

Small streams

Sockeye salmon have different biological features, depending on the habitat they occupy

Habitat conditions vary among locations in watersheds

August 2000, NASA

Salmon habitat is also different among locations in the ocean

Locations where juvenile salmon enter the ocean

NOAA

Portfolio effects derive from intact and viable habitat

Bristol Bay, Alaska Pacific Northwest

* 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