Coho salmon (Oncorhynchus kisutch) usually spend two years in the ocean and return to spawn as three-year-olds (Waldvogel personal communication 1996), although some males return after only a few months. In the Smith River, adult upstream migration and spawning begins in November and December. Compared to chinook, coho typically utilize smaller streams and prefer smaller spawning gravel. However, there is overlap between coho and chinook spawning habitat. After emerging from the redd, coho generally remain in the river for their first year. As yearlings, they may migrate downstream in the spring, and enter the ocean when five to six inches long. In many river systems, coho enter the ocean in fall as subyearlings while only one to three inches long (Sandercock 1991). Likewise, in some river systems of the Pacific Northwest, coho salmon fry rear in estuaries (Hassler 1987). It is not known if either of these life history patterns exist, or once existed, on the Smith. A relatively consistent proportion of the coho males from any given age class return from the ocean after only a few months as "jacks". Therefore, the number of "jacks" provides an estimate of the size of a particular cohort that is still in the ocean (Waldvogel personal communication 1996).

Coho are present in high numbers in Mill Creek (Rellim Redwood Company 1994, Table 29) and have been observed in at least ten tributaries and subtributaries of the lower river including Rowdy Creek, Morrison Creek, Little Mill Creek, Sultan Creek, Peacock Creek, and Clarks Creek. Coho also have been observed in certain upper tributaries including Patrick Creek, Shelley Creek, Rock Creek, and Jones Creek (Figure 4 will be added, Scriven in progress). However, with the exception of Mill Creek and Rowdy Creek, coho are not present every year (Scriven personal communication 1997, Moyer personal communication 1996).

Because coho are abundant in Mill Creek but are found in low numbers in other scattered tributaries, careful management of Mill Creek is needed. Maintaining Mill Creek as a highly productive "source" habitat is critical because other areas may lack sufficient populations or habitat quality to survive independently. "Stray" coho from the Mill Creek source population are very important in survival of the overall coho "meta-population" throughout the watershed. Coho from Mill Creek can be instrumental in recolonization of the river system. If the habitat in Mill Creek is degraded, the larger meta-population of the species may be threatened.

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