Coho salmon

"Coho" redirects here. For other uses, seeCoho (disambiguation).

Coho salmon
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Salmoniformes
Family:	Salmonidae
Genus:	Oncorhynchus
Species:	O. kisutch
Binomial name
Oncorhynchus kisutch (Walbaum,1792)

Thecoho salmon(Oncorhynchus kisutch;Karuk:achvuun) is aspeciesofanadromousfishin thesalmonfamilyand one of the fivePacific salmonspecies. Coho salmon are also known assilver salmon(or "silvers" ) and is often sold asmedium red salmon.The scientific species name is based on theRussiancommon namekizhuch(кижуч).

Description

Coho salmon fromOregon

During theiroceanphase, coho salmon have silver sides and dark-blue backs with spots on their back and upper tail lobe.During their spawning phase, theirjawsandteethbecome 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 7 to 11 pounds (3.2 to 5.0 kg), occasionally reaching up to 36 pounds (16 kg).Size can vary depending on age and geographic location.Males tend to be slightly larger than females.Mature adults also develop a large kype (hooked beak) which is used to attract a mate during spawning, with males having a more pronounced kype than females.The coho salmon's lower jaw can be distinguished by a light shade at its superior edge.

Reproduction

Dead salmon, shortly after spawning. Live fish right after spawning will show the same white, rotting flesh shortly before death

Once the mature coho has reached three or four years old, it swims up freshwater rivers and streams tospawn(reproduce). Once reaching a suitable location, females dig a divot in the riverbed by flexing their tails and loosing rocks from the riverbed, repeating 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 releasesmilt(sperm) onto the eggs. Unchosed 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 beginsemelparity,whereby they stop eating and deteriorate to death.

Life stages

See also:Salmon run

The eggs hatch in the late winter or early spring after six to seven weeks in theredd.Once hatched, they remain mostly immobile in the redd during thealevinlife stage, which also lasts for six to seven weeks.Alevin no longer have the protective egg shell, orchorion,and rely on theiryolksacs for nourishment during growth. The alevin life stage is very sensitive to aquatic and sedimental contaminants. When the yolk sac is completely resorbed, the alevin leaves the redd.Young coho spend one to two years in their freshwater natal streams, often spending the first winter in off-channel sloughs, before transforming to thesmoltstage. Smolts are generally 100–150 mm (3.9–5.9 in) and as theirparrmarks fade and the adult's characteristic silver scales start to dominate. Smolts migrate to the ocean from late March through July. Some fish leave fresh water in the spring, spend summer inbrackishestuarineponds, and then return to fresh water in the fall. Coho salmon live in salt water for one to three years before returning tospawn.Some precocious males, known as "jacks", return as two-year-old spawners. Spawning males develop kypes, which are strongly hookedsnoutsand largeteeth.

• 
  Fingerling
• 
  Male ocean phase coho
• 
  Male freshwater phase coho
• 
  Breeding male

Range

The traditional range of the coho salmon runs along both sides of the North Pacific Ocean, fromHokkaidō,Japanand eastern Russia, around theBering Seato mainlandAlaska,and south toMonterey Bay, California.Coho salmon have also been introduced in all theGreat Lakes,as well as many landlocked reservoirs throughout theUnited States.A number of specimens, (more than 20), were caught in waters surroundingDenmarkandNorwayin 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.

Human uses

Freshly caught coho

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 21,000tonnesin all.Coho salmon are the backbone of the Alaskantrollfishery, though the majority are caught by the net fishery (gillnetandseine fishing). They average 3.5% by fish and 5.9% by weight of the annual Alaska salmon harvest.The North Pacific yields ofpink salmon,chum salmonandsockeye salmonare about 15 times larger by weight.

Game fish

In North America, coho salmon is agame fishin fresh and salt water from July to December, especially with lightfishing tackle.It is one of the most popular sport fish in thePacific Northwestof the United States and Canada. Its popularity is due in part to the reckless abandon which it frequently displays chasingbaitandlurewhile insalt water,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 toanglerson 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 springchinookandsockeye salmonhave 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 severalindigenous peoples,who would also use it to trade with other tribes farther inland. The coho salmon is also a symbol of several tribes, representing life and sustenance.

Ecology

In their freshwater stages, coho feed on plankton and aquatic invertebrates in the benthos and water column, such asChironomids,midgelarvae, and terrestrial insects that fall into the water.Upon entering the marine environment, they switch to a diet of plankton and fish, with fish making up most of their diets after a certain size.Adult coho feed on a vast variety of prey items that depend on the region they reside in during their second year at sea. Spawning habitats are small streams with stable gravel substrates.

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.

Conservation

See also:Steelhead and salmon distinct population segments

Coho salmon,Tillamook State Forest,Oregon

The U.S.National Marine Fisheries Service(NMFS) has identified seven populations, called Evolutionary Significant Units (ESUs), of coho salmon inWashington,Oregonand California.Four of these ESUs are listed under the U.S.Endangered Species Act(ESA).These are the LowerColumbia River(threatened), Oregon Coast (threatened), Southern Oregon and NorthernCaliforniaCoasts (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.

ThePuget Sound/Strait of GeorgiaESU 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 theSecretary of Commerce,listed as threatened the Southern Oregon/Northern California Coast coho salmon ESU.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 asEl Niño,which causes extremes in annual rainfall on the northern California coast), predation by theCalifornia sea lionand Pacificharbor seal,and commercial timber harvesting.

More than 680,000 coho salmon returned to Oregon in 2009, double that of 2007. TheOregon Department of Fish and Wildliferequired 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 fatterplankton,which, along with greater outflows ofColumbia Riverwater, fed the resurgent populations. The 2009 run was so large, food banks were able to freeze 40 tonnes (39 long tons; 44 short tons) for later use.

See also

• Pre-spawn mortality in coho salmon
• Inbreeding in fish

References

• "Oncorhynchus kisutch".Integrated Taxonomic Information System.Retrieved24 January2006.
• Froese, Rainer; Pauly, Daniel (eds.) (2005)."Oncorhynchus kisutch"inFishBase.10 2005 version.
• "Coho salmon in the Great Lakes".Archived fromthe originalon 2007-09-23.Retrieved2007-09-14.

External links

• Use of three microhabitats by juvenile coho salmon in Jordan Creek during the winter, 2004-2005 / by Ryan J. Briscoe.Hosted by theAlaska State Publications Program.