are. Stream cleaning continued through the mid-1970s, in an attempt to reduce flooding and improve fish migration.
The National Marine Fisheries Service (NMFS) reviewed the past destruction, modification and curtailment of freshwater habitat in 1996. NMFS found that the factors for decline of habitat on the west coast were due to dams (blocking juvenile and adult passage), water withdrawal (stranding fish entraining juveniles and increasing temperatures), flood control (stream channelization and simplification), logging and agriculture (loss of LWD, sedimentation, loss of riparian vegetation, habitat simplification), mining (gravel removal dredging and pollution) and urbanization (vegetation removal pollution channelization increased runoff, habitat simplification). Lichatowich (1989) confirms that habitat loss is a significant contributor to stock declines in coastal coho salmon streams.
Gregory and Bisson (1997) showed that habitat degradation has been associated with 90% of documented extinctions or declines of pacific salmon stocks. California has reportedly lost 89% of the states riparian woodlands due to various land use practices (Kreissman1991). Fisk et al. (1966) showed a loss of over 1,600-km of stream had been destroyed or damaged by 1966.
Large deep pool habitat, critical for coho salmon survival has declined on the West Coast by 58% on National Forest Lands, and by 80% in surveyed Oregon coastal streams (FEMAT 1993, Murphy 1995). Logging, agriculture, urbanization, grazing, and mining have led to large reductions in essential summer and winter rearing habitat for coho salmon. Habitats essential for coho survival are now rare in many streams i.e. backwater pools, side channels, off-channels, deep lateral sour pools, dam pools, and stream margins where LWD and boulders form deep cold water pools. In California loss of deep water pool habitat leaves coho salmon vulnerable to high instream summer water temperatures, winter flood events and predation by birds and mammals, due to lack of cover.
Habitat protection is the key to conservation and recovery of wild coho salmon, because the technological ability to restore habitats once they are damaged is severely limited, mostly due to our lack of understanding of how to best provide for coho salmon and the need for improvements in the technology. Although millions of dollars have been invested in artificial habitat alterations in attempts to improve habitat for coho and other fish, there have been few examples of successful large-scale recovery of coho populations attributable to man made habitat improvements. Unfortunately the cost of restoring a significant portion of altered streams using these technologies is prohibitive (Pearcy et al. 1992). In many streams in the Pacific Northwest existing technology for channel restoration has failed to treat the causes of habitat degradation (e.g., Klamath Basin Fisheries Task Force 1991). Furthermore, because the largest share of coho habitat is surrounded by private land (The Wilderness Society, report in preparation), recently proposed reforms in federal forest management (FEMAT 1993), will not be sufficient to safeguard this species from further decline and widespread extinction across a significant portion of its range.
Adverse Ocean Conditions
Ocean conditions have generally been deteriorating for coho in the lower 48 states during the past two decades (Lawson 1993), and there is little indication that favorable conditions will return in the near future. Most variation in ocean mortality of coho salmon apparently occurs during the first few weeks of ocean life (Pearcy and Fisher 1988), so that near-shore conditions during late spring and early summer along the coasts of Washington, Oregon, and California dramatically affect year-class strength. Evidence that upwelling along the Pacific Coast of North America is driven by 40-60-year cycles in wind patterns. Following an interval of generally favorable conditions in 1945-1975, upwelling declined along the Oregon coast and marine survival of coho salmon declined at a simil