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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 [email protected] 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? Salmon habitat in Bristol Bay 9 major rivers North Pacific Ocean Bristol Bay each with many populations L.A. Rogers Wood River Commercial fisheries for sockeye salmon in Bristol Bay have been sustained for over 120 years - record catches have occurred within the last 20 years 50,000,000 Number of sockeye salmon caught in Bristol Bay (1893-2010) Togiak 45,000,000 Ugashik Egegik Commercial Commercialcatch catch 40,000,000 Nushagak Naknek-Kvichak 35,000,000 30,000,000 25,000,000 20,000,000 15,000,000 10,000,000 5,000,000 data from ADFG Year 2003 1993 1983 1973 1963 1953 1943 1933 1923 1913 1903 1893 0 Different dynamics in stocks of Bristol Bay sockeye produce portfolio effects in fisheries Bristol Bay river stocks Sockeye salmon returns to Bristol Bay rivers Relative run size size run Relative size run Relative 1010 11 0.1 0.1 0.01 0.01 1956 1961 1966 1956 1961 1966 1971 1971 1976 1976 1981 1981 Year Year 1986 1986 1991 1991 1996 1996 2001 2001 2006 2006 Age diversity Salmon returns to Bristol Bay are two times more reliable than the individual components of the portfolio Total return (relative) Bristol Bay Major rivers 1 2 3 Streams All the same age 10 10 10 10 1 1 1 1 0. 1 0. 1 0. 1 0. 1 0. 01 0. 01 1 1960 year 2010 0. 01 0. 01 1 1 1 Eroded portfolio 2.2 times more variable than the Bristol Bay salmon portfolio How does reliability affect people dependent on fisheries? http://www.absc.usgs.gov/research/Fisheries/Lake_Clark/subsistence.htm The front line at Egegik Variability in salmon increases the rate of fisheries closures 100 90 Fisheries are closed 4 years every century Bristol Bay (intact portfolio) 80 70 60 Number of returning salmon 50 40 average 30 20 minimum spawners 10 0 100 90 X X X Bristol Bay (eroded portfolio) X Fisheries are closed 40 times every century 80 70 60 50 40 30 20 10 0 X X X X X XX XX X X XX XXX X X X X X XX X Time (100 years) XXXX X X Sockeye salmon have different biological features, depending on the habitat they occupy Lake beaches Small streams L.A. Rogers Habitat conditions vary among locations in watersheds Salmon habitat is also different among locations in the ocean Locations where juvenile salmon enter the ocean August 2000, NASA Portfolio effects derive from intact and viable habitat Bristol Bay, Alaska Pacific Northwest NOAA * 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