The coho salmon ( Oncorhynchus kisutch; Karuk: achvuun
Description
During their
ocean phase, coho salmon have silver sides and dark-blue backs with spots on their back and upper tail lobe.
During their spawning phase, their
and
teeth become hooked. After entering fresh water, they develop bright-red sides, bluish-green heads and backs, dark bellies and dark spots on their backs. Sexually maturing fish develop a light-pink or rose shading along the belly, and the males may show a slight arching of the back. Mature adults have a pronounced red skin color with darker backs and spots, with females having darker shades than males.
Coho salmon average 20 to 28 inches (50.8 to 71 cm) and , occasionally reaching up to .
Reproduction
Once the mature coho has reached three or four years old, it swims up freshwater rivers and streams to spawn (reproduce).
Coho will swim up streams as far as they are physically able, usually reaching areas of water as little as deep. Females seek out beds of gravel at the head of a riffle, where they turn on their sides to dig a nest with movements of their tail, creating round or oval depressions roughly the same lengths and width as the fish.
This process is repeated for up to seven nests, each called a redd. Females become extremely aggressive with each other over nesting sites, and with males until these are dug. Males then fight for the right to mate. Once a female has chosen a mate, usually the largest male, she lays her eggs onto the redd, while he simultaneously releases
milt (sperm) onto the eggs. Unchosen males also sneak in to release milt at this time. Once all eggs are laid, she covers them with rocks and pebbles using her tail. The adults then begin
semelparity, whereby they stop eating and deteriorate to death.
Life stages
The eggs hatch in the late winter or early spring after six to seven weeks in the redd.
[ Once hatched, they remain mostly immobile in the redd during the alevin life stage, which also lasts for six to seven weeks.]
File:Coho salmon fingerling (SC) 1.JPG|Fingerling
File:Lake Washington Ship Canal Fish Ladder pamphlet - ocean phase Coho.jpg|Male ocean phase coho
File:Lake Washington Ship Canal Fish Ladder pamphlet - male freshwater phase Coho.jpg|Male freshwater phase coho
Range
The traditional range of the coho salmon runs along both sides of the North Pacific Ocean, from Hokkaidō, Japan and eastern Russia, around the Bering Sea to mainland Alaska, and south to Monterey Bay, California.
Natural reproduction in introduced areas is generally low. Limited self-sustaining populations are recorded in Lake Superior and Michigan, but the salmon does not reproduce naturally in the Wisconsin tributaries of Lake Michigan and relies on stocking to maintain a large population. The species is no longer stocked in Lake Erie, although stray individuals from elsewhere in the Great Lakes are caught on occasion. Efforts to establish the species in Connecticut began in the 1800s, but were discontinued when the species failed to establish a stable population. Introductions in Connecticut and Delaware also failed to found permanent populations.
Over twenty specimens were caught in waters surrounding Denmark and Norway in 2017. Their source is currently unknown, but the salmon species is farmed at several locations in Europe, making it probable that the animal has slipped the net at such a farm.
Ecology
In their freshwater stages, coho feed on plankton and aquatic invertebrates in the benthos and water column, such as Chironomidae, midge larvae, and terrestrial insects that fall into the water.
Salmonid species on the west coast of the United States have experienced dramatic declines in abundance during the past several decades as a result of human-induced and natural factors.
Human uses
Fisheries
The total North Pacific harvest of coho salmon in 2010 exceeded 6.3 million fish, of which 4.5 million were taken in the United States and 1.7 million in Russia. This corresponds to some 21,000 in all.[ Annual Statistics 2010: Commercial salmon catch by species and country North Pacific Anadromous Fish Commission Statistical Yearbook. Retrieved 2015 March 16. These numbers do not include fish taken in Russian waters by foreign fleet.] Coho salmon are the backbone of the Alaskan troll fishery, though the majority are caught by the net fishery (gillnet and seine fishing). They average 3.5% by fish and 5.9% by weight of the annual Alaska salmon harvest.[(Alaska Seafood Marketing Institute, 2003, p. 2)] The North Pacific yields of pink salmon, chum salmon and sockeye salmon are about 15 times larger by weight.
Game fish
North America, coho salmon is a game fish in fresh and salt water from July to December, especially with light fishing tackle. It is one of the most popular sport fish in the Pacific Northwest of the United States and Canada.[L. Blair Holtby, Ronald K. Kadowaki, and Kent S. Simpson. 1992. Factors Affecting the Vulnerability of Juvenile Coho ( Oncothynchus kisutch) and Chinook Salmon ( O. tshawytscha) in a Saltwater Sport Fishery. Canadian Journal of Fisheries and Aquatic Sciences. 49
]
/ref> Its popularity is due in part to the reckless abandon which it frequently displays chasing Fishing bait and Fishing lure while in seawater, and the large number of coastal streams it ascends during its spawning runs. Its habit of schooling in relatively shallow water, and often near beaches, makes it accessible to Fisherman on the banks, as well as in boats.
It is also pursued by fly fishermen in salt water.
Nutritional value
Ocean-caught coho is regarded as excellent table fare. It has a moderate to high amount of fat, which is considered to be essential when judging taste. Only spring Chinook salmon and sockeye salmon have higher levels of fat in their meat. When smoking coho it is best to use a cold-smoking rather than hot-smoking process, due to their lower fat content compared to sockeye and chinook.
Cultural tradition
Historically coho, along with other species, has been a staple in the diet of several indigenous peoples, who would also use it to trade with other tribes farther inland.[William I Atlas, Natalie C Ban, Jonathan W Moore, Adrian M Tuohy, Spencer Greening, Andrea J Reid, Nicole Morven, Elroy White, William G Housty, Jess A Housty, Christina N Service, Larry Greba, Sam Harrison, Ciara Sharpe, Katherine I R Butts, William M Shepert, Elissa Sweeney-Bergen, Donna Macintyre, Matthew R Sloat, Katrina Connors, Indigenous Systems of Management for Culturally and Ecologically Resilient Pacific Salmon ( Oncorhynchus spp.) Fisheries, BioScience
/ref>
]
Conservation
The U.S. National Marine Fisheries Service (NMFS) has identified seven populations, called Evolutionary Significant Units (ESUs), of coho salmon in Washington, Oregon and California.[
][
] These are the Lower Columbia River (threatened), Oregon Coast (threatened), Southern Oregon and Northern California Coasts (threatened), and Central California 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 Sound/Strait of Georgia ESU in Washington is an NMFS "Species of Concern".[
] Species of Concern are those species for which insufficient information prevents resolving the U.S. National Oceanic and Atmospheric Administration's concerns regarding status and threats and whether to list the species under the ESA.
On May 6, 1997, NMFS, 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. These reductions are due to natural and man-made changes, including short-term atmospheric trends (such as El Niño, which causes extremes in annual rainfall on the northern California coast), predation by the California sea lion and Pacific harbor seal, and commercial timber harvesting.
More than 680,000 coho salmon returned to Oregon in 2009, double that of 2007. The Oregon Department of Fish and Wildlife required volunteers to herd fish into hatchery pens. Some creeks were reported to have so many fish, "you could literally walk across on the backs of coho," claimed a Portland television station. Lower temperatures in 2008 North Pacific waters brought in fatter plankton, which, along with greater outflows of Columbia River water, fed the resurgent populations.[Galbreath, P. F., Bisbee, M. A., Dompier, D. W., Kamphaus, C. M., & Newsome, T. H. (2014). Extirpation and Tribal Reintroduction of Coho Salmon to the Interior Columbia River Basin. Fisheries, 39
/ref> The 2009 run was so large, food banks were able to freeze for later use.][
]
See also
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Pre-spawn mortality in coho salmon
-
Inbreeding in fish
Footnotes
External links
