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Chinook salmon (Oncorhynchus tshawytscha)
Chinook were, and are, the most abundant salmon species in the Klamath basin, and are the backbone of important commercial, sport, Tribal and subsistence harvests. Genetically, Chinook salmon in the Klamath are split into two groups, known as the Southern Oregon and Coastal (SOCC) Evolutionarily Significant Unit, and the Upper Klamath and Trinity Rivers ESU. The SOCC ESU spawns only in the lower river estuary during the fall and is connected to other runs in coastal streams in Southern Oregon and Northern California. The Upper Klamath and Trinity Rivers ESU includes all other Chinook spawning in the basin, and is split into three runs: fall, late-fall, and spring. More commonly, however, Chinook in the Klamath are grouped into spring or fall runs, and there is science supporting a genetic separation of spring run Chinook into their own ESU (NRC 2004). Note "Chinook" is the only salmon species whose common name is capitalized, in honor of Chinook Tribal history.
Spring-run Chinook
Threat status: Wild spring run Chinook once numbered over 100,000 and spawned throughout the Klamath Basin, but are now limited to a small population remnant on the Salmon River and Wooley Creek that numbers from 150-1,500 fish (Campbell and Moyle 1991, Barnhart 1994). The National Marine Fisheries Service considered managing spring-run Chinook as a distinct ESU because of their unique life history and genetics but ultimately chose against it (Myers et al. 1998). If Klamath spring run Chinook were assigned to their own ESU, they would most likely be considered threatened or endangered.
Distribution: Spring-run Chinook had significant populations spawning in at least the Shasta, Scott, Salmon, Sprague, and Williamson Rivers and many larger tributary creeks. The Sprague and Williamson River populations were cut off by the construction of Copco dam in 1917, and the Shasta River population went extinct the same year Dwinnell Dam was built on the Shasta in 1926. Like the Scott River population, the Shasta River spring Chinook were heavily impacted by hydraulic mining, diversions, and fishing. Landslides associated with clear cut logging in the 1960s further decimated spring run Chinook in these streams. Currently, the Salmon River run of spring Chinook is the only wild population still in existence, and its viability is being examined as a potential source of stock for the reintroduction of spring Chinook into the Upper Basin. The Trinity Rivers hatchery releases over one million juvenile spring-run Chinook annually, and all spring-run fish returning to spawn in the Trinity are considered hatchery fish (NRC 2004).
Ecology: Spring run Chinook adults enter the Klamath from April to July, and hold in deep pools for 2-4 months before spawning while their gonads develop. This allows them to spawn and develop in upstream reaches of tributaries often inaccessible to fall-run Chinook because of low flows and high temperatures in the lower reaches during fall (Moyle 2002). Spawning peaks in October, fry emerge from March to June, and stay in the cool headwaters through the summer, sharing habitat with coho (NRC 2004). Like coho, spring Chinook are vulnerable to human-caused habitat degradation, because they require clear, cold pools free of sedimentation for holding over the summer as adults, and cool headwater streams for maturing over the summer as fry (NRC 2004).
Current Science and Restoration: The Salmon River Restoration Council is actively tracking and supporting the Salmon River run of spring Chinook. Dr. Jerri Bartholomew, a researcher at Oregon State University, is actively investigating the fish parasites Ceratomyxa shasta and Parvicapsula minibicornis that threaten spring and fall Chinook on the Klamath.
Fall run Chinook
Threat status: Though fall-run Chinook are not listed threatened or endangered, their numbers have declined considerably from historic levels, and current returns may be up to 60% hatchery-produced. Since 1978, escapement (number of fish returning to spawn) has numbered between 30,000 and 230,000 fish. Historic accounts indicate that total river and ocean harvest of these fish may have been up to 250,000 fish in the early 20th century (NRC 2004).
Distribution: Fall-run Chinook also continue to spawn in the mainstem Klamath and most major tributary creeks and rivers. Wild fall-run Chinook were thought to have returned abundantly to the Shasta River and to the Upper Klamath Basin. The Iron Gate and Trinity Rivers hatcheries produce 7-12 million fish per year, nearly 90% of which are fall-run juvenile Chinook.
Ecology: Fall run Chinook juveniles spend less than a year in freshwater, meaning they head to the ocean before water quality conditions become too challenging on the Klamath. Though they were historically "summer-run" fish, entering the river to spawn around July, they now enter in the fall, perhaps to avoid summer water temperatures and associated disease outbreaks on the river. Adults spawn and die within 2-4 weeks of entering the Klamath between September and November. Fry emerge from the gravel between February and April, depending on stream temperatures. After emergence juveniles disperse downstream and hold in stream margins and vegetated areas for varying amounts of time, eventually making their way to the estuary and then the ocean. Fall run Chinook utilize habitat on the mainstem Klamath and in tributary streams. (NRC 2004)
Current Science and Restoration:Dr. Jerri Bartholomew, a researcher at Oregon State University, is actively investigating the fish parasites Ceratomyxa shasta and Parvicapsula minibicornis that threaten spring and fall Chinook on the Klamath.
Links & References:
Campbell, E.A. and P.B. Moyle. 1991. Historical and recent population sizes of spring-run chinook salmon in California. Pp 155-216 in Proceedings of the 1990 Northeast Pacific Chinook and Coho Salmon Workshop: Humboldt State University, Arcata, CA, September 18-22, 1990, T.J. Hassler, ed. Arcata, CA: California Cooperative Fishery Research Unit, Humboldt State University.