 rates on Oregon coastal coho substantially during the past decade. However, there has been no evidence of increased spawner escapement during this period, suggesting that fishing curtailment is at best merely keeping pace with rapid habitat deterioration and declining productivity of coho populations (Pearcy et al. 1992). In other words, environmental change is likely driving sustainable harvest rates downwards as fast as, or perhaps faster than, catch has been reduced. Unfortunately, the lack of adequate monitoring of habitat precluded certainty in assessing the relative roles of environmental deterioration and overfishing (Pearcy et al 1992).
Current methods of forecasting and in-season adjustment of fishing are insufficient to ensure sustainable harvest rates and wild fish escapement. Greater factors of safety for escapement numbers and better indicators of determining freshwater and marine survival and distribution factored with a clear understanding of habitat loss may give a more accurate model for determining harvest.
Annual catch of coho salmon in California ocean and troll fisheries ranged from 100,000 to more than 650,000 fish in the late 1960s and 1970s (PFMC 1978). Fishing effort in this region is directed primarily toward hatchery coho and to the much more abundant chinook salmon. Aside from this very large landed harvest of coho, which includes a mixture of hatchery and wild fish, heavy incidental coho mortality may occur during the chinook season. Additional mortality of wild coho is incurred in freshwater fisheries. Spawning escapement of wild coho in California and southern Oregon is not monitored or calculated in Pacific Fishery Management Council (PFMC) harvest decisions, and fishery mortality on viability and distribution coho salmon populations throughout the southern portion of their range. Although California and southern Oregon populations of coho salmon are lumped with Oregon coastal populations by PFMC for purposes of harvest management, these southern populations were not considered in 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