 PFMCs assessment of overfishing of Oregon coastal coho (Pearcy et al. 1992).
The current and past policy of attempting to conserve coho salmon by focusing primarily on the regulation of harvest has failed. Curtailment of fishing can do little than temporarily delay extinctions that are ultimately caused by deterioration of habitat (Lawson 1993).
On the other hand, given that freshwater and marine habitats apparently continue to decline, it is difficult to establish sustainable levels of a coho fishery. In view of critically low escapement levels and signs of extensive local extinction of populations in recent years, as well as little indications of recovery of freshwater habitats in the near future, severe curtailment on fishing appears to be a prudent temporary measure.
As a formerly abundant species becomes fragmented and dwindles in abundance, it becomes vulnerable to the impacts of genetic introgression and hybridization. Hybridization can be aggravated by habitat change or barriers to movement that reduce the opportunity for isolation between coexisting species, or by introduction of hatchery-origin or non-native fish whose life history patterns, behaviors, or distribution are unlike those of the fisheries indigenous to the site. Hybridization causes the loss of inter-population diversity, possibly jeopardizing the evolutionary future of the species.
Bartley et al. (1990) and Bartley (1990) have reported hybridization between coho and fall-run chinook salmon in the Klamath River basin. Hybrid individuals were detected by electrophoretic techniques. In one case coho and chinook salmon adults were apparently inadvertently crossed by fish culturists at the Irongate hatchery and the offspring released. In another case hybridization was likely a result of artificial blockage and crowding of large numbers of adult salmon in a tributary just below Lewiston Dam and hatchery in the Trinity River (Bartley et al. 1990). Two hybrid salmon were recovered in the ocean fishery, so at least some hybrids survive and grow to large size (Bartley et al. 1990). Their ability to mature and produce viable offspring remains unknown.
If first generation hybrids fail to produce viable offspring, at a minimum they can function to dilute the reproductive effectiveness of coho salmon that mate with them, as well as potentially competing with viable coho salmon individuals for food and space (Hindar et al. 1991). Transfer of genes from chinook to coho salmon via hybridization in Trinity River could underlie a detected increase in the susceptibility of (putative) coho salmon to infectious hematopietic necrosis virus (IHNV). Until recently coho salmon were considered resistant to this disease.
Monitoring has been insufficient to determine the possible incidence and long-range effects of hybridization problems. This is especially important given the widespread and increasing occurrence of situations where wild coho salmon populations are closely intermingled with hatchery salmon or artificially induced concentrations of salmon of multiple species on spawning grounds.
Failure to Adequately Monitor Wild Populations and Habitat
The failure of state and federal agencies to adequately monitor wild populations of coho salmon is a serious problem for protection and management of salmonids. In California, there is virtually no systematic monitoring of wild coho escapement by state or federal agencies. Wild coho in California are included in ocean harvests, but there has been no attempt to ascertain the effects of these harvests and mitigate their potential effects on wild populations.
No adequate monitoring of freshwater or ocean habitat, or yearly survival of coho in artificial propagation programs has been done to date. There are a variety of propagated fish species that may directly or indirectly impact coho salmon. In California there are only rudimentary monitoring and regulation of artificial propagation programs for a variety of fish species that directly or indirectly impact coho salmon. These programs are conducted by both large and small hatcher