then die. Run and spawn timing of adult coho salmon vary between and within coastal and 

 Columbia River Basin populations. Depending on river temperatures, eggs incubate in "redds" 

 (gravel nests excavated by spawning females) for 1 .5 to 4 months before hatching as "alevins" (a 

 larval life stage dependent on food stored in a yolk sac). Following yolk sac absorption, alevins 

 emerge from the gravel as young juveniles, or "fry." and begin actively feeding. Juveniles rear in 

 fresh water for up to 15 months, then migrate to the ocean as "smolts" in the spring. Coho 

 salmon typically spend two growing seasons in the ocean before returning to their natal streams 

 to spawn as 3 year-olds. Some precocious males, called "jacks," return to spawn after only 6 

 months at sea. ■ ■ 



SPECIES DISTRIBUTION 



During this century, indigenous, naturally-reproducing populations of coho salmon are believed 

 to have been eliminated in nearly all Columbia River tributaries and to be in decline in numerous 

 coastal streams in Washington. Oregon, and California. Coho in at least 33 stream/river systems 

 have been identified by agencies and conservation groups as being at moderate or high risk of 

 extinction. In general, there is a geographic trend in the status of west coast coho salmon stocks, 

 with the southernmost and easternmost stocks in the worst condition. 



MAJOR IMPACTS 



Logging, agricultural and mining activities, urbanization, stream channelization, dams, wetland 

 loss, water withdrawals, and unscreened diversions for irrigation have contributed to the decline 

 of the Central California coast coho ESU. 



Long-term trends in rainfall and marine productivity associated with atmospheric conditions in 

 the North Pacific Ocean may have a major influence on coho salmon production as well. Much 

 of the Pacific coast has experienced drought conditions during the past 8 years, a situation which 

 has undoubtedly contributed to the decline of many salmonid populations. El Niiio ocean 

 conditions cause decreases in primary and secondary productivity and changes in prey and 

 predator species distributions. 



Potential problems associated with non-native coho salmon stocks that have been introduced as 

 broodstock in hatcheries and widely transplanted in many coastal rivers and streams in central 

 California include genetic impacts on indigenous, naturally-reproducing populations, disease 

 transmission, predation of wild fish, difficulty in determining wild stock status due to incomplete 

 marking of hatchery fish, depletion of wild stock to increase brood stock, and replacement rather 

 than supplementation of wild stocks through compefifion and continued annual introduction of 

 hatchery fish. 



Marine harvest of coho salmon occurs primarily in nearshore waters off British Columbia. 

 Washington. Oregon, and California. Recreafional fishing for coho salmon is pursued in 

 numerous streams throughout the central California coast when adults return on their fall 

 spawning migration. The confounding effects of habitat deterioration, drought, and poor ocean 

 conditions make it difficult to assess the degree to which recreational and commercial harvest 

 have contributed to the overall decline of coho salmon in West Coast rivers. 



56 



