ons) 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 historical records of occurrence of coho in 582 California streams, ranging from the Smith River near the Oregon border to the Big Sur River on the Central Coast. More recent surveys available for 42% of these streams indicate that 46% have lost their populations (Brown and Moyle, 1991). The Wilderness Society estimates in California, that coho salmon are extinct in 26% of their range, endangered in 22%, and threatened in the remaining 52% of the historic range.
Generally, the further south a stream is located on the California coast, the more likely it is to have lost its coho population (Brown and Moyle, 1991). Coho Salmon are rare in the Sacramento River even though several attempts have been made to establish runs (Hallock and Fry, 1967). It is likely that runs occurred at one time at least in tributaries to San Francisco Bay, if not in more interior streams. In the 1960s coho salmon were also widely distributed on the central coast surveys in the 1970s showed 12 streams from San Mateo to Monterey County, had documented runs of coho salmon (Hassler, Sullivan, Stern 1991). By the 1980s these populations had been extirpated in 8 streams, and with reestablishment of coho in Gazos Creek, there are now coho in 5 streams with small populations (Dave Hope personal communication).
EVOLUTIONARY SIGNIFICANT UNIT
The existence of stocks, as defined by Ricker (1972), is no longer in doubt. The subdivision of a species into local populations which posses genetic differences that are adaptive is the fundamental basis of the stock concept, and it is this concept that must be incorporated into management if fishery reserves are to be restored and maintained. (MacLean and Evans, 1981.) We recognize that many instances will arise were there is doubt. In those cases, we believe the prudent manager will recognize the stock in question until such time that enough evidence is collected to show otherwise. Since the loss of a stock is an irreversible loss, its existence should be given the benefit of any doubt. (Nehlsen, Williams a