 of the coho salmon in California has been well documented by Shapovalov and Taft (1954) and Hassler (1987). Most coho salmon return to their parent streams after spending two years in the ocean (up to three years in Alaska). Jack males may, however, return after one growing season in the ocean (at age 2 years), but most fish in California return after two growing seasons in the ocean (age 2 years). In California, spawning migrations begin after heavy late fall or winter rains breach the sand bars to the mouths of coastal streams, allowing the fish to move into the streams. However, migration typically occurs when stream flows are either rising or falling, not necessarily when streams are in full flood.
In the Klamath River, the coho will run between September and late-December, with peak runs occurring during October and November. Spawning itself occurs mainly in November and December (U.S. Fish and Wildlife Service, 1979). In Waddell Creek, peak spawning is between January 15 and February 15 and spawning migrations often do not begin until late November or December (Shapovalov and Taft, 1954). In Oregon and south of San Francisco streams, spawning can occur as late as March, if drought conditions delay rains or runoff (Sandercock, 1991, Smith, 1991).
Coho salmon migrate and spawn mainly in small coastal streams that flow directly into the ocean or in the tributaries of large rivers. Females choose the spawning sites (redds), usually near the head of a riffle (at the tail of a pool) at, or slightly upstream of the hydraulic control, where the water changes from smooth to turbulent flow and there is a medium to small gravel substrate (1/2 to 4.4). The flow characteristics at the location of the redd usually ensure good aeration, and the circulation facilitates fry emergence from the gravel. Each female builds a series of redds, moving upstream as she does so she deposits a few hundred eggs in each. Thus, spawning may take about a week to complete and a female can lay between 1,400 to 7,000 eggs. There is a positive correlation between fecundity and size of females. Both males and females die soon after spawning.
Eggs hatch after 8-12 weeks of incubation, the time being inversely related to water temperature. Hatchlings remain in the gravel until their yolk sacs have been absorbed, 4-10 weeks after hatching. Upon emerging, they seek out swallow water along the stream margins. Initially they form schools, but as they grow bigger the schools break up and the juveniles (parr) set up individual territories. The larger parr tend to occupy the heads of pools (Chapman and Bjornn, 1969). As the fish continue to grow, they move into deeper water and expand their territories until, by July and August, they are in deep pools. Territory size for coho is inversely related to the amount of food available.
Between December and February, winter rains results in increased stream flows and by March, following peak flows, fish again feed heavily on insects and crustaceans and grow rapidly. Toward the end of March and the beginning of April they begin to migrate downstream and into the ocean. Out-migration in small California streams typically peaks from mid-April to mid-May, if conditions are favorable. Migratory behavior is related to rising or falling water levels, size of fish, day length, water temperature, food densities and dissolved oxygen levels. At this point, the outmigrants are about one year old and 10-13 centimeters in length. The fish migrate in small schools of about 10-50 individuals. Parr marks are still prominent in the early migrants, but later migrants are silvery, having transformed into smolts.
After entering the ocean, the immature salmon initially remain in near-shore waters close to their natal stream. They gradually move northward staying over the continental shelf. Coho salmon can range widely in the north Pacific. The movements of California fish were poorly known until the Pacific States Marine Fisheries Commissions (PSMFC 1994) Regional Mark Information System. It appears that recent coded wire tag data indicat