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The Coho salmon, Oncorhynchus kisutch, (from the Russian кижуч kizhuch) is a species of anadromous fish in the salmon family. Coho salmon are also known as silver salmon or "silvers". It is the state animal of Chibamarker, Japanmarker.

Description

During their ocean phase, Coho have silver sides and dark blue backs. During their spawning phase, the jaws and teeth of the coho become hooked, and they develop bright red sides, bluish green heads and backs, dark bellies with dark spots on their back. Sexually maturing coho develop a light pink or rose shading along the belly and the males may show a slight arching of the back. Mature coho salmon have a pronounced red skin color with darker backs and average 28 inches in length and 7 to 11 pounds in weight, although coho weighing up to 36 pounds have been reported. Mature females may be darker than males, with both showing a pronounced hook on the nose.

Reproduction

The eggs hatch in the late winter or early spring after 6 to 7 weeks in the redd. Once hatched, they remain mostly immobile in the redd as the alevin life-stage, which lasts for 1–2 weeks. The alevins no longer have the protective egg shell, or chorion, and rely on their yolk sac for nourishment during growth. The alevin life stage is very sensitive to aquatic and sediment contaminants. When the yolk sac is completely resorbed by the alevin it will swim up out of the redd. Young coho spend one to two years in their freshwater natal streams,often spending the first winter in off-channel sloughs, before undergoing a transformation to the smolt life-stage. Smolts are generally 100-150 mm and their parr marks are faded and the silver scales characteristic of the adult life-stage start to dominate. Smolts migrate to the ocean in late March through July. Some fish leave fresh water in the spring, spend summer in brackish estuarine ponds and then migrate back into fresh water in the fall. Coho salmon live in the salt water for one to three years before returning to spawn. Some precocious males known as "jacks" return as two-year-old spawners. Spawning males develop a strongly hooked snout and large teeth.File:Lake Washington Ship Canal Fish Ladder pamphlet - ocean phase Coho.jpg|Male ocean phase CohoFile:Lake Washington Ship Canal Fish Ladder pamphlet - male freshwater phase Coho.jpg|Male freshwater phase CohoImage:Coho on Bumper.jpg|Freshly caught coho

Conservation

The U.S. National Marine Fisheries Service has identified seven populations, called Evolutionary Significant Units (ESUs), of coho salmon in Washingtonmarker, Oregonmarker and California. Four of these ESUs are listed under the U.S. Endangered Species Act (ESA). These are the Lower Columbia River (threatened), Oregon Coast (threatened), Southern Oregon and Northern California Coasts (threatened), and Central Califorina Coast (endangered). The long-term trend for the listed populations is still downward, though there was one recent good year with an increasing trend in 2001.

The Puget Soundmarker/Strait of Georgiamarker ESU in Washington state is a U.S. National Marine Fisheries Service "Species of Concern". Species of Concern are those species about which the U.S. National Oceanic and Atmospheric Administration has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the ESA.

On May 6, 1997, the National Marine Fisheries Service, on behalf of the Secretary of Commerce, listed as threatened the Southern Oregon/Northern California Coast coho salmon ESU. 62 Fed.Reg. 24588. The coho salmon population in the Southern Oregon/Northern California region has declined from an estimated 150,000 – 400,000 naturally spawning fish in the 1940s to fewer than 10,000 naturally producing adults today. The dramatic reduction in the coho salmon population has been due to many natural and man-made conditions, including long-term trends in atmospheric conditions, such as El Niño, which causes extremes in annual rainfall on the northern California coast; the predation of coho salmon by the California Sea Lion and Pacific Harbor Seal; and commercial timber harvesting.

Many groups are actively involved in conservation of the coho salmon and their habitat. The Salmon Protection and Watershed Network (SPAWN) has achieved great success over the last 10 years protecting the coho salmon population in the San Geronimo Creek and Lagunitas Creek Watersheds of West Marin, California, with a combination of grassroots activism, habitat restoration, policy development and biological monitoring. The coho salmon in the San Geronimo Creek and Lagunitas Creek Watersheds are the southernmost, stable population of wild coho in California and account for almost 30% of the state's coho in <1% of="" the="" state's="" designated="" coho="" habitat.=""></1%>

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