lmon from different California streams that have been extensively planted (Bartly, 1991). Recent studies of spawning escapement showed that 63 populations showed significant decline and only 2 showed increases. This data is similar to that found in Washington. ( Konkel and McInyre 1987). In 1890 Sacramento River summer and fall runs of coho salmon were noted in the press, but by 1950, no viable populations could be found (Hallock and Fry 1967).
The upper Klamath River had runs of 1,600 coho before the 1920s; these coho are now extinct (Klamath River Task Force). The California Department of Fish and Game summarized recent data and determined that most remaining coho salmon were hatchery fish although some wild coho may still remain in small tributaries. This same report concluded coho salmon in California, including hatchery stocks, could be less than 6% of their abundance in the 1940s, and have experienced at least a 70 % decline in numbers since the 1960s, and many populations have been eliminated and others have runs only 1 out of 3 years, indicating two brood years have been lost and extinction is imminent.
In 1993, Pacific Rivers Council, Brown and Moyle (1991) estimated that naturally spawned adult coho salmon (regardless of origin) returning to California streams were less than 1% of their abundance at mid-century, and indigenous, wild coho salmon populations in California were a probably 1,000 individuals. Brown and Moyle (1991) also found that 46% of the California streams that historically supported coho salmon no longer supported runs. Brown et al. (1994) found in central California that the proportion of streams with coho salmon present was higher in recent surveys (1995-96), moving from 47% to 57%, but northern California streams with coho present, fell from 63% to 52%.
Brown and Moyle (1991, Brown et al. 1994) estimated average coho salmon spawning escapement in the central California coast ESU as 6,160 naturally spawning coho salmon and 332 hatchery spawned coho salmon from the period from 1987 to 1991 (Table 7). Of the naturally spawning coho salmon, 3,880 were from tributaries in which supplementation occurs (Noyo River and coastal streams south of San Francisco). Only 160 fish in the range of this range ESU (all in Ten Mile River) were identified as native stock (lacking a history of supplementation with non-native hatchery stocks).
Populations south of San Francisco were estimated at around 10,000 returning adults in the late 1800s, these populations had fallen to 100 or fewer in 1990 (Hope 1993). These populations have rebounded due to efforts enhance survival through curing populations of Bacterial Kidney Disease and careful propagation and release of fry. The returning adults are now estimated to be between 500- 1000 on good brood years (D. Hope pers. com.). Evaluation of these streams by Nehlsen in 1991 identified stocks in small coastal streams north of San Francisco as at moderate risk of extinction, and those small streams south of San Francisco at high risk of extinction. Higgins et al. (1992) looking closely at streams in Sonoma County north identified the Gualala River at high risk of extinction.
Historic data on adult coho salmon runs are available for 186 streams. Recent data for 133 of those 186 streams show 71 no longer have runs of coho salmon, while 62 still maintained runs of adult coho salmon (Brown et al. 1994).
NATURE OF THE THREAT
In reviewing the following description of the factors that threaten the continued existence of coho salmon in California, it should be noted that this decline has been continuing for over 50 years. The cumulative effects of all human induced impacts has so depressed the populations that even factors such as natural predation have taken on critical significance. Human development and its associated impacts are primarily responsible for the decline of coho salmon populations. Habitat loss in both freshwater and ocean, overexploitation, disease and a host of other human related influences has created a critical situation for the continued viability of coho s