Klamath Falls Field Station
Coho salmon (Oncorhynchus kisutch)
Coho salmon, or “silver” salmon, are anadromous, meaning that they spend the majority of their lives in the ocean and return to freshwater to spawn. Like other Pacific salmonids, coho salmon are semelparous, meaning that they die after spawning. Coho salmon are not as large as Chinook salmon but can grow to 30 inches in length and weigh in excess of 20 pounds. The majority of individuals rear in freshwater habitats for about a year before smolting and migrating to the ocean, then spend another 18 months in the ocean before returning to spawn as adults. This leads to distinct three-year cycles in the numbers of returning adults. However, coho salmon exhibit a variety of life histories; for example, some juveniles remain in freshwater habitats for up to two years, and some small jack males return to spawn at two years of age after only six months in the ocean. Spawning adults deposit eggs and milt into areas of gravel substrate modified into nest depressions known as redds. After hatching, rearing coho salmon prefer clear, deep, cool waters with abundant overhead cover, including spring-influenced tributaries and pools. Such habitats are often limiting, particularly during summer months when flows are reduced and water temperatures can exceed their physiological upper limits.
Coho salmon were historically abundant and widely distributed throughout the lower Klamath River Basin. Although they are reported to have used freshwater habitats all the way to the Oregon-California border, there is little evidence that they penetrated very far into the Upper Klamath Basin. Coho salmon populations in the Klamath River Basin are severely reduced from historical levels and are listed as federally threatened, part of the Southern Oregon/Northern California Coasts Evolutionarily Significant Unit. Klamath River coho salmon make their spawning run primarily in October and November and peak spawning occurs in November and December. The early part of the spawning run is dominated by males and the later part of the run is dominated by females. Juvenile coho salmon in the Klamath River watershed smolt and migrate to the ocean primarily in April and May.