iles are .25 to 1.5 feet per second depending on habitat. High turbidity is detrimental to emergence, feeding and growth of young coho (Emmett, et al, 1991). Young and adult coho salmon are found over a wide range of substrates, from silt to bedrock.
California rivers having coho salmon, from Redwood Creek (in Humbolt County) southward, drain 1,500- 3000 high Coast Range, an area underlain by easily eroded sedimentary rocks of the Franciscan Formation (California State Lands Commission 1993). To the north, the Smith and Klamath River Basins cut through the Coast Range to drain the Cascade Mountains as well. Maximum elevations in this area are typically 3,000-6, 000. Rivers from the Smith River south to the Mattole River exhibit peak flow in late January or early February, while rivers farther south have peak flows in late February (Figure 2). Duration of peak flows in rivers south of the Mattole are much shorter than those farther north (Figure 3), although both areas experience relatively low flows during the summer and early fall figure 4. Annual precipitation levels are also much higher along the west side of the Coast Range in northern California (60 to 80) than they are farther south (25 to 60), or the dry interior along the east slope of the coast range (25 to 60) (figure 9). Central California has a relatively short rainy season compared to regions farther north. Annual snowfall in the southern Mattole River basin averages 2 feet, while the Klamath Mountains average 2 feet to above 10 feet. Maximum summer stream temperatures (18 to 26 degrees C), average maximum summer temperatures (Figure 7), and winter minimum temperatures (Figure 8) are similar along the California coast from the San Lorenzo River to the California/Oregon border. Winter stream temperatures in central California are generally warmer by an average of 10 degrees F, while differences in average annual sunshine in central California are higher by 200 to 600 hours per year.
The California coastal area is dominated mostly by (Sequoia Sempervirons) redwood forests, giving way to Douglas fir/hardwood forests farther inland. This forest type forms the dominant coastal vegetation in coho dominated landscapes south to Monterey, at elevations between 100 to 2500.
Vegetation in the upper basins in northern California rivers is adapted to a more arid climate than basins closer to the coast. Other vegetation types that exist in some upper river basins are Klamath montane, coastal montane, Blue oak-digger pine, and chaparral. South of the Mattole River, upper basins are not as arid, and the vegetation is primarily redwood with patches of mixed evergreens and mixed hardwoods, and coastal prairie-scrub around the San Francisco Bay area.
HISTORIC AND CURRENT DISTRIBUTION
Coho salmon are a widespread species of pacific salmon, occurring in most major river basins around the Pacific Rim from central California to Korea and northern Hokkaido, Japan. In the United States distribution is from Point Hope, Alaska to the San Lorenzo River in Santa Cruz County. Recently published investigations have reported that a number of local populations of coho salmon in Washington, Oregon, Idaho, and California have become extinct and that abundance of many others is depressed (e.g., Brown and Moyle1991, Frissel 1993, Nehlsen et al. 1991 ).
In California, coho salmon were distributed in all accessible streams on the coast north of Big Sur. Some inland populations still occur on the Eel and Klamath River systems (Hassler 1987). Principal populations are located in the Smith, Klamath, Trinity, Mad, Noyo, and Eel rivers, with smaller populations in coastal streams south to the San Lorenzo River. In the Eel River system, coho formerly ascended 390 kilometer (246 miles) of stream in 60 tributaries (Mills, 1983) of the South Fork Eel, the lower main stem Eel River, and the Van Duzen River (Brown, 1987). Annual runs on the Eel River in the early years have been estimated at over 40,000 fish; current runs are probably less than 1000 fish (Brown and Moyle, 1991). Brown and Moyle (1991) found