The Benefits of a Diverse Portfolio and Threats to Future Returns: Lessons Learned from the Bristol Bay Sockeye Salmon Fishery

The value of a portfolio is a function of its assets, the degree to which they co-vary through time, and their contributions to the aggregate.  Collectively, the geographically distinct stocks of sockeye salmon returning to Bristol Bay, Alaska, comprise the largest stock complex of sockeye salmon in the world.  The composition of these stocks is as diverse as the freshwater ecosystems where they spawn and rear, and the local adaptations across the stock complex has led to a more stable fishery.   Since the 1950s the commercial catch of Bristol Bay sockeye has averaged over 20 million fish, despite significant environmental variability.  With proper management, the Bristol Bay portfolio has remained both diverse and sustainable.  Potential threats to the long term productivity exist because of the homogenization of distinct life-histories, and loss of local adaptations. These immediate threats are largely from proposed large-scale mining that would alter the habitat and require storage of toxic mine tailings, both of which threaten productivity and diversity of the portfolio. The lessons from Bristol Bay sockeye salmon are that a diverse portfolio of stocks leads to less volatile and more sustainable returns, and that loss of diversity would likely reduce the socio-economic value of this fish.