FEATURE ARTICLE
Preserving Salmon Biodiversity
The number of Pacific salmon has declined dramatically. But the loss of genetic diversity may be a bigger problem
Phillip Levin, Michael Schiewe
Safe or Sorry
Uncertainty about the importance of local adaptation at small spatial scales, about the rate of adaptive evolution or simply about the value of diversity could be used to justify a continuation of research rather than action to preserve salmonid populations now. That would be unfortunate: Too much remains unknown about the importance of biodiversity to discount it at present. So we favor a precautionary approach. That is, people should consider the consequences of being wrong about their assumptions. If biodiversity proves less important than anticipated, so be it. But if biodiversity turns out to be more critical than is now believed, we want to ensure that salmon will not have been sent down the path to extinction without the genetic resources to escape.
Conservation biologists have generally argued that biodiversity is valuable for two reasons. First, it leads to a greater abundance of the species in question, because different populations can exploit different habitats and resources in unique ways. Second, it fosters enhanced long-term stability by spreading the risk and providing redundancy in the face of unpredictable catastrophes. Both arguments apply well to salmon—and strongly support the precautionary approach to conserving their biodiversity. The many salmon ESUs utilize their freshwater habitats in very distinct ways: For example, some sockeye spawn in lakes, others in rivers. And salmon often spawn and migrate at different times and to different parts of the ocean. Furthermore, genetic diversity offers insurance against the vagaries of climatic fluctuations that can affect salmon populations dramatically.
Fisheries scientists know why salmon populations are on the brink—the complex network of dams, the failure to regulate the salmon harvest adequately, the destruction of salmon habitat and an over-reliance on hatcheries have all contributed to varying degrees. Saving Pacific salmon will clearly require immediate action that will include economic sacrifice, societal discipline and a commitment to a science-based recovery strategy—all at a very significant cost to the people of the affected regions.
But people must acknowledge that there is no clear line between sustainability and extinction for salmon, because their populations change so much over time and space. The current quest for a precise definition of how much habitat salmon need, how many can be safely harvested, or how little biological diversity needs to preserved is not consistent with the needs of the species. For millennia the salmon have "hedged their bets" against major catastrophes, such as ice ages, continental uplifts and volcanic eruptions. They have done so by maintaining a diversity of populations and habitats—in short, they have developed a rich and varied set of genes. Salmon should be allowed to continue pursuing their survival strategy—a strategy that worked before humans arrived on the continent and, if these fish manage to survive, will work long after we are gone.
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