Coho salmon, also known as silver salmon, are a type of salmon native to Western North America as well as North Eastern Russia and Northern Japan. An anadromous fish, Coho salmon are born in freshwater streams and then migrate to the ocean where they inhabit the Northern Pacific Ocean. At sexual maturity, Coho salmon return to the streams that they were born in, spawn, and then die. Unlike other types of anadromous fish, such as steelhead and green and white sturgeon, Coho salmon are not repeat spawners as their lifecycle ends after spawning is complete.
Coho salmon belong to the order Salmoniformes which includes all types of salmon, trout, steelhead, smelt, and whitefish. Salmon and trout, when referred to as a group, are known as salmonids, as this helps separate them from the other types of fish that are also found in this order.
Coho salmon are known scientifically as Oncorhynchus kisutch. An adult Coho salmon that is living in the ocean can be 12-24 inches long and will usually weigh 6-12 pounds. Larger specimens have be caught to weigh up to 31 pounds and have a length of 38 inches but smaller sizes are more typical of this species of salmon. The coloration of an ocean going Coho will have a dark black or blue back with silver sides and spots on the upper part of the tail fin. Cohos of both sexes that have returned to freshwater to spawn will develop red coloration on their heads and sides, but only the males will develop the characteristic long hooked jaws with large sharp teeth known as a kype. The kype is used by males to battle each other for the chance to spawn with the females.
The lifecycle of Coho salmon begins in a stream bed in late fall to mid-winter where the female makes a nest in the gravel called a redd. She then deposits her eggs in the redd while the male fertilizes them simultaneously. Coho salmon can lay up to 4,500 eggs in a single redd. After the female and male have completed the spawning process, both fish die and their bodies are eaten by other water inhabitants as well as bears and birds of prey. As long as the eggs are not eaten by other predators, they will hatch in the spring and the fry will live off of their yolk. The fry will continue to live near the gravel or under areas that provide little disturbance such as among a tangle of wood or logs under the water. During this time, they will sustain themselves by eating invertebrates found in the water on at the surface. Juveniles will usually spend one year in the streams before heading out to the ocean.
While growing in the ocean, Coho salmon will eat larger prey, including other small fish. It is at this time that they will reach their mature size. Coho will live in the ocean for 3 years before returning to the streams of their birth to spawn and then die.
Coho salmon are an important species of salmon both commercially and ecologically. Seventy-five percent of the Coho salmon caught in the United States come from Alaska where this and other species of salmon are still plentiful. In other areas, such as the California, Oregon and Southern Washington coasts and waterways, the spawning grounds of the Coho salmon are designated as critical habitats as the numbers of returning Coho have been dwindling steadily since the 1990s.
In 1873, Coho salmon were introduced into the Great Lakes. Being non-native, the introduced Coho soon died without spawning, but were later reintroduced in 1966 as a game fish. Successful spawns are minimal in this different environment, so the population of introduced Coho is kept up in the lakes by stocking. Successful spawns that do occur are subject to predation by the native fishes and other animals of the Great Lakes. Those that do survive to be adults must compete for food with the other native fish.
Coho salmon are an important species not only commercially, but also as an ecological indicator of the health of the environment. Proper care and understanding of the fish’s needs in order to spawn successfully need to be carried out to keep this fish returning season after season.