ar rate (Pearcy et al. 1992). Coho along the Oregon and California coasts may be especially sensitive to upwelling patterns, because these regions lack extensive bays, straits, and estuaries to buffer oceanographic effects. Assuming Ware and Thompsons hypothesis is correct, ocean conditions are likely to remain generally unfavorable at least through the next two decades.
Evidence suggests there have been extensive changes in marine food webs during this century, and these changes may reduce survival of coho salmon at sea. The abundance of two species comprising a large share of the pelagic biomass of the Northeast Pacific Ocean, Pacific sardines and hake, have collapsed during this century, and failed to recover during the most recent period of favorable ocean conditions. Overfishing of these species during low-productivity periods may have contributed to their collapse and failure to recover, and resulting changes in the marine food web (i.e., predation shifts from pelagic to near-shore and migratory species) could adversely affect coho and other anadromous fishes.
Assuming oceanographic and atmospheric relationships of recent centuries hold in the future, anticipated climate warming during the next several decades is likely to cause continued adversity, or perhaps progressive deterioration of marine habitat for coho salmon. This could forestall or curtail the future recovery of ocean conditions postulated by Lawson (1993).
Given that manipulation of ocean and atmospheric behavior is beyond human capability, the deterioration of ocean conditions clearly makes the quality of freshwater habitat more critical for short-term productivity and long-term survival of the species (Lawson 1993).
Overfishing is often cited as a principle factor causing decline of salmon runs. However, there are few historical or recent records to indicate that curtailment of fishing has lead to increased spawning abundance of coho salmon. For example, curtailment of fishing seasons has been thought to have reduces harvest-related mortality 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