Fish and Aquatic Conservation



illustration of a Coho_salmon

Coho salmon

Onchorhynchus kisutch (Walbaum, 1792)

Cool Facts

Coho salmon average 8 lbs. or 3.6 kg but may weigh as much as 35 lbs. or 16 kg. The life span of Pacific coho is variable. The oldest recorded age for coho salmon is 5 years. These fish occur in the ocean or in lakes. Young fish migrate at night into lakes or the ocean. Fish that remain in freshwater for more than two years and reach sexual maturity are called “residuals” and never spawn.

SIZE: Coho salmon average 24 inches (9.4 cm) long, but specimens have been recorded as long as 42.5 inches (108 cm).

RANGE: Coho salmon in the North Pacific range from the Anadyr River in Russia, southward towards Hokkaido, Japan. Coho range from Point Hope in Alaska, southward to Chamalu Bay in Baja California and all the way into Mexico.

HABITAT: Coho salmon are an anadromous species that primarily spend their adult life in salt water and then migrate into freshwater to spawn. The exceptions to this strategy include the residuals that are described in the above paragraph. In general, adult coho salmon migrate from the sea or lake, then school at the river mouths and proceed upstream when precipitation significantly increase water flows. Upon arriving at spawning areas, which are normally small tributaries with stable gravel substrates, the female will find a spot and dig a pit with her tail. While preparing the spawning pit, the female is accompanied by a male that wards off other male coho salmon that swim near the pit. Upon completing the pit, the female coho salmon drops into the pit to first deposit the eggs and then the male coho salmon will follow the female and fertilize the eggs with his milt.

DIET: Young coho salmon which inhabit lakes and rivers eat mainly insects. When migrating to the sea, the young salmon dine on planktonic crustaceans. As they grow and move further out to sea, they begin to hunt larger forage species such as fish, squid and jellyfish.

Natural History

Coho salmon are an anadromous species and migrate from the ocean to their freshwater natal streams to spawn. Coho salmon spawn only once and then die. This single spawning life history strategy is called semelparity.

Most male coho salmon return to their natal streams to spawn after three years in the ocean, but some male only spend two years at sea and then return to their natal spawning streams. These two year old males, better known as “jack males” have a unique spawning strategy. Because of their smaller size, jack males get in very few battles with other, larger spawning males over prime spawning habitat, because they are not considered a threat to the other larger males. When the larger males become embroiled in a turf war over a piece of prime spawning real estate, the smaller jack male will sneak over the redd and release his milt while two or more larger males are engaged in combat. This unique spawning strategy is called a “sneaking” strategy.

Coho salmon spend approximately the first half of their life rearing and feeding in streams and freshwater tributaries and the remaining half of their lifetime foraging in estuarine and marine waters of the Pacific Ocean.

Conservation

Currently there is one Endangered population segment of coho salmon, three Threatened population units of coho salmon and one Species of Concern population segment of coho salmon delineated under the Endangered Species Act.

In 1999, Critical Habitat was designated for the Central California Coast and Southern Oregon/Northern California Coast coho salmon. In February 2016, Critical Habitat was also designated for Lower Columbia River coho salmon. The Alaskan coho salmon fishery has been certified by the Marine Stewardship Council as well managed and sustainable.