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Coho salmon (Oncorhynchus kisutch)
Coho salmon are declining as a species throughout the West Coast. Of all the salmon species, they are particularly vulnerable because they require colder water temperatures and make extensive use of the side channels, log-jam pools, and shallow stream margins often impacted by the channelization and loss of riparian vegetation associated with agriculture and development. Klamath River coho are part of what's called the Southern Oregon-Northern California Coast Evolutionarily Significant Unit (or SONCC ESU). Once abundant throughout the Klamath basin, coho have declined significantly over the last 50 years, and can now be found in much smaller numbers wherever they still have access to suitable habitat.
Threat status: Southern Oregon-Northern California coho are listed as "threatened" on the federal Endangered Species List, and are considered "endangered" by the states of California and Oregon. Less than 70% of streams where coho historically lived in the Klamath Basin still contain small populations of coho, and in some places, such as the Trinity River, wild coho stocks are at as little as 4% of their previous numbers (NRC 2004). It is also difficult to tell to what extent hatchery production of coho supplement wild stocks, though one study estimated that 90% of adult coho returned to Iron Gate and Trinity River hatcheries for spawning (Brown 1994).
Distribution: Coho historically occurred throughout the Klamath and its tributaries, though locations above the California-Oregon border are poorly documented due to the inability of early observers to distinguish between coho and the more common Chinook (NRC 2004). The National Marine Fisheries Service has identified the Shasta, Scott, Salmon and Trinity Rivers, as well as 6 creeks between Iron Gate Dam and Seiad Valley, 13 creeks between Seiad Valley and Orleans, and 27 creeks between Orleans and the mouth of the Klamath as important coho habitat (NMFS 2002). The Oregon Department of Fish and Wildlife is planning for natural recolonization of coho at least to Spencer Creek after fish passage is gained through PacifiCorp's dams. Because of its abundance of cold springs, the Shasta was probably an important location for coho, though numerous diversions and loss of riparian vegetation have taken their toll (NRC 2004).
Ecology: Klamath coho typically have a three year life history in which eggs are laid in the fall, juveniles rear for 14-18 months in fresh water, and then mature in the Pacific for another 18 months before returning to spawn. A small percentage of males return to spawn early, in their second year, and these are known as "jacks." Most spawning takes place in the coarse gravels of forested tributaries. Eggs hatch in 2-3 months, and alevins (hatchlings with yolk sacs attached) stay among the gravel fro another 4-10 weeks, where they are susceptible to scouring from high flows or smothering from silt. The alevins emerge as non-territorial fry (30-35 mm) and live in shallow stream margins from February to April. When the fish reach 50-60 mm they are considered juveniles and stake out and defend territory in the pools and runs of forested streams with dense cover from logs and woody debris. They require clear, well-oxygenated water and low temperatures (12-14 degrees Celsius). Juveniles may range into the mainstem Klamath, but generally avoid the mainstem's relatively high night-time temperatures, as well as habitat competition with and predation by Chinook and steelhead, many of whom are hatchery-produced and therefore more robust (NRC 2004).
Current Science and Restoration: The Shasta Valley Resource Conservation District is actively working to address habitat issues on the Shasta River, a key tributary for coho on the Klamath. The Nature Conservancy and the University of California at Davis are also studying unique foodweb interactions on the Shasta that may explain the historical abundance of coho on this river and shed light on how to restore it. The Scott River Resource Conservation District and Watershed Council are planning an extensive groundwater monitoring study to determine how agricultural groundwater pumping may be contributing to drastically reduced flows and loss of coho in the Scott River. Removal of PacifiCorp's four lower Klamath River dams would allow coho to recolonize historical habitat in Upper Klamath tributaries. Klamath Riverkeeper tracks and comments on agency plans and processes that affect "take" (or killing) of coho, as well as advocates for land management that returns clear, cold water to vital coho tributaries such as the Scott and Shasta Rivers.
Links & References:
Brown, L.R., P. B. Moyle, and R. M. Yoshiyama. 1994. Historical decline and current status of coho salmon in California. N. Am. J. Fish. Manage. 14(2):237-261.
National Research Council. 2004. Endangered and Threatened Fishes in the Klamath River Basin: Causes of Decline and Strategies for Recovery. Washington, DC: The National Academies Press. 397 pages.