Klamath Falls Field Station
Chinook salmon (Oncorhynchus tshawytscha)
Chinook salmon, or “king” salmon, are the largest of the Pacific salmonids, with adults exceeding 40 pounds in weight. Spawning adults are powerful swimmers and some populations migrate hundreds of miles into freshwater to reach spawning areas. Like other Pacific salmonids, Chinook salmon are anadromous and semelparous, meaning that they spend the majority of their lives in the ocean, return to freshwater to spawn, and die after spawning. As a species, Chinook salmon exhibit a wide variety of life history types. Juveniles can spend anywhere from three months to two years in freshwater habitats and adults can remain in the ocean for one to six years before returning to spawn. Chinook salmon populations are divided into “runs” (e.g., spring, fall) depending on the time of year adults return to spawn, and a given river can support multiple runs. Runs are further distinguished as either stream-type or ocean-type, although the distinction is not always simple. In general, stream-type spawners run into freshwater in spring or summer as immature fish and complete their maturation in freshwater before spawning. Juveniles of stream-type runs typically spend a year or more in freshwater habitats. Ocean-type spawners typically run in summer and fall and spawn soon after arriving at spawning areas. Juvenile ocean-type fish usually spend less than a year in freshwater habitats, sometimes as little as a few months. Spawning adults deposit eggs and milt into areas of gravel and small cobble substrate modified into nest depressions known as redds. After hatching, rearing Chinook salmon occupy a variety of habitats and smolting and outmigration to the ocean can be rather protracted depending on the run.
Chinook salmon populations were and still are the most abundant anadromous fish in the Klamath River Basin. In the past, Chinook salmon ascended the Klamath River into the Upper Klamath Basin, spawning in tributaries as far upstream as the Williamson, Sprague, and Wood Rivers. Chinook salmon in the Klamath River Basin are primarily ocean-type fall-run populations that depend on mainstem river habitats and large tributaries. Most adults return to spawn between September and November at three years of age, and are thus not as large as individuals in other runs that stay at sea for longer periods of time. The populations are reduced from historical levels and are supplemented by hatchery production, but nonetheless support important commercial, recreational, and tribal fisheries. Although they are not federally listed under the Endangered Species Act, NOAA NMFS recognizes two Evolutionarily Significant Units that cover the Klamath River Basin populations: the Southern Oregon and Northern California Coastal (downstream of the confluence with the Trinity River) and the Upper Klamath and Trinity Rivers (both rivers upstream of the confluence). Spring-run Chinook salmon populations were once abundant and widespread in the Klamath River Basin, but have been severely reduced and currently only persist in a few streams in the lower Basin. Spring-run Chinook salmon in the Klamath River Basin are not recognized as an ESU distinct from the fall-run populations.