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
Hatcheries
Hatcheries (where fry are raised from eggs) have become the foundation of efforts to preserve the salmon fishing industry—and in some cases the species themselves. Each year, North American facilities release more than five billion juvenile salmon; on the Columbia River alone, hatcheries produce about 200 million fish. But the benefits of all this work have yet to be demonstrated. Indeed, this program may well be a contributing factor in the long-term decline of salmon.
How so? To answer that question, one needs to understand how the system operates. The raising of Pacific salmon is sometimes called "sea ranching." Fish remain in hatcheries until they are juveniles, when they are released into the adjoining river or stream. They soon swim to the Pacific to feed on the "ocean pasture." The salmon that survive typically return to the hatchery in which they were raised, although some do stray and spawn in the wild. The risk of changing the salmonid gene pool as a result of such practices was once thought to be minimal, because these fish typically experience natural conditions for most of their lives. Recent research, however, suggests that the artificial propagation of salmon can permanently alter genetic makeup and ultimately reduce the viability of wild populations.
A 1999 review by Reginald Reisenbichler and Steve Rubin of the U.S. Geological Survey dramatically highlights this notion. They found that the survival of hatchery-raised steelhead released into a river in Oregon was about 20 percent lower than that of their wild counterparts. In a separate study, Ian Fleming and Mart Gross of the University of Toronto determined that coho bred in hatcheries tend to be less aggressive than wild coho and thus have less success spawning. The ability to avoid predators, the timing of reproduction and their degree of territoriality also vary between hatchery and wild salmon. When hatchery-raised fish stray, they can pass on their genes to others. And although the hypothesis is still the subject of much research, many studies suggest that such interbreeding between hatchery and wild fish results in offspring that are less fit to survive.
Clearly, conservation managers need to rethink the traditional role of hatcheries. We anticipate that there will be a place for them. But the people who run hatcheries must focus their attention on the production of salmon that are more like their wild counterparts, and they must find other ways to minimize adverse effects on wild populations.
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