o be relatively well adapted to the empty habitat by virtue of geographic proximity and environmental similarity. Given sufficient time they can successfully restore the former range of the species. Because the life span of a single population is likely to be less than a few thousand years or perhaps centuries, maintenance of a broad distributional range and an expansive network of such population is critical for the long-term survival of the species as a whole. Large-scale fragmentation and collapses of range, such as coho have exhibited in California and the Columbia Basin this century, indicate that metapopulation structure and function is breaking down catastrophically, and that remaining populations face greatly increased risk of extinction (Frissell 1993).
Southern populations of coho salmon may be unusually well adapted to future, warmer and intensively human-altered environments. This indicates that the populations of coho salmon disappearing most rapidly are those which may be of greatest utility to ecosystems, fish managers, and fish harvesters in the future.
The loss of the coho salmon over significant portions of its range curtails or eliminates the functional role of the species in the ecosystem. In freshwater, coho and other salmon species are prey items for numerous aquatic and terrestrial predator and scavenger species and may contribute significantly to the nutrient budget of aquatic and riparian ecosystems (Houston 1983, Cederholm et al. 1989). At sea, and in freshwater, coho salmon function as a significant, if not primary food resource for a incredible array of predatory animals. Thus the loss of coho salmon is felt throughout the full range of the aquatic and terrestrial ecosystem.
For the present, our lack of understanding of how subtle natural genetic signatures create success or failure in a specific stream, makes it imperative that we save all existing runs of coho salmon to preserve the genetics for future conservation efforts. Loss of any population causes an irreversible blow to the genetic pool of a species and will jeopardize the recovery of the species forever. The present large-scale collapse of coho salmon and the fragmentation of this species range clearly demonstrates that conservation biology must take precedence immediately if we are to save this and other collapsing salmonid populations.
It is exactly the progressive decline, attrition, and lack of genetic diversity in all of our coho salmon populations over their entire range that threaten the future of this species. The loss of single population hinders the entire species ability to survive environmental change, and reduces the ability to evolve and persist into the future.
Artificial Propagation and Loss of Between-Population Diversity
Hatchery-origin fish have not been used to successfully re-build or re-establish coho salmon populations in the region. In general, there are very few (if any) examples of hatchery programs that led to successful re-building of wild populations of Pacific salmon within their native range ( Miller et al. 1990). Despite this history, some hatchery proponents continue to make optimistic projections of the future benefits of fish culture, with little or no scientific evidence to back up their claims. When successful in terms of producing hatchery fish, artificial propagation breeding tends to reduce, rather than increase, diversity of wild populations.
The potential and demonstrated adverse genetic effects of artificial propagation of salmonid populations have been discussed in several recent reviews (Hindar et al. 1991, Waples 1991). The capture of brood stock itself can be destructive of small or declining wild populations. Due to small broodstock populations, pre-spawning mortality during capture or transport, unnatural mating combinations, differential viability of gametes in artificial situations, disease, and artificial selection, wild brood stock typically contribute little genetic diversity to subsequent generations of hatchery fish (Bartley et al. 1992). The taking of larger numbers of wild fis