es that at least 65-92% of Californias coho salmon feed in the oceans off our coast. This is also true of Oregons coho as most coho caught off the California coast in ocean fisheries were reared in Oregon streams (natural and hatchery). In 1990 for instance, commercial and recreational fisheries caught 112,600 coho, a number that greatly exceeds the present production capabilities of California populations alone. (A. Baracco, California Department of Fish and Game, personal communication.)
Oceanic coho tend to school together. Although it is not known if the schools are mixed, consisting of fish from different streams, fish from different regions are found in the same general areas. Adult coho salmon are primarily piscivores, but shrimp, crabs and other pelagic invertebrates can be important foods in some areas.
Spawning sites are typically at the head of riffles or tail of pools where there are beds of loose, silt free, course gravel and where cover exists nearby for adults. Unlike other salmon species, coho salmon redds can be situated in substrates composed of up to 10% fines (Emmett, et al, 1991), but in general, spawning success and fry survival are favored by very clean gravel consisting of less then 5% fines (California Department of Fish and Game 1991). Spawning depths are 4-21 inches, with water velocities of 6.5 to 26.2 feet per second (Hassler1987). Optimal temperatures for development of embryos in the gravel are 43-50 degrees F, although eggs and alevins can be found in 40-70 degree F water. Dissolved oxygen levels should be above 8 mg/l for juveniles (Emmett, et al. 1991).
Juveniles prefer deep (greater than 3 feet), well shaded pools with plenty of overhead cover; highest densities are typically associated with logs and other woody debris in the pools or runs. Juveniles require water temperatures that do not exceed 71-77 degrees F for extended time and oxygen and food (invertebrates) levels remain high. Preferred temperatures are 50-59 degrees F (Hassler, 1987); preferred water velocities for juveniles 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 Sempervir