A member of the Salmonidae family, the coho salmon is an extremely adaptable ﬁsh that occurs in nearly all of the same waters as does the larger chinook salmon, but it is a more spectacular fighter and the most acrobatic of the Paciﬁc salmon. It is one of North America’s most important sport- and commercial ﬁsh, especially to the Paciﬁc coast of North America.
IdentificationThe body of the coho salmon is elongate and somewhat compressed, and the head is conical. For most of its life (in saltwater or lake, as well as newly arrived in a spawning river), this species is a dark metallic blue or blue-green above, becoming silvery on the sides and the belly. There are small black spots on the back and on the upper lobe of the caudal ﬁn.
It can be distinguished from the chinook salmon by its lack of black spots on the lower lobe of the tail and the white or gray gums at the base of the teeth; the chinook has small black spots on both caudal lobes of the tail, and it has black gums.
Spawning adults of both sexes have dark backs and heads and maroon to reddish sides. The males turn dusky green above and on their heads, bright red on their sides, and blackish below. The females turn a pinkish red on their sides. The male develops a prominent double-hooked snout, called a kype, with large teeth, which makes closing the mouth impossible.
SizeCoho do not attain the size of their larger chinook brethren and in most places are caught around the 4- to 8-pound mark. The all-tackle world record is a 33-pound, 4-ounce specimen from the Great Lakes. Fish to 31 pounds have been caught in Alaska, where the average catch is 8 to 12 pounds and 24 to 30 inches long.
Life history/BehaviorLike all species of Paciﬁc salmon, coho are anadromous. They hatch in freshwater rivers, spend part of their lives in the ocean, and then spawn in freshwater.
Adult male sea-run coho salmon generally enter streams when they are either 2 or 3 years old, but adult females do not return to spawn until age 3. All coho salmon, whether male or female, spend their ﬁrst year in the stream or river in which they hatch.
The timing of runs into tributaries varies as well. Coho salmon in Alaska, for example, enter spawning streams from July through November, usually during periods of high runoff. In California, the runs occur from September through March, and the bulk of spawning occurs from November through January.
Run timing has evolved to reﬂect the requirements of speciﬁc stocks. In some streams with barrier falls, adults arrive in July when the water is low and the falls are passable. In large rivers, adults must arrive early, as they need several weeks or months to reach headwater spawning grounds.
Run timing is also regulated by the water temperature at spawning grounds: Where temperatures are low and eggs develop slowly, spawners have evolved early run timing to compensate; conversely, where temperatures are warm, adults are late spawners.
Little is known of the ocean migrations of coho salmon. Evidently, there are more coho salmon in the eastern Paciﬁc and along the coast of North America than in the western Paciﬁc. High-seas tagging shows that maturing southeast Alaska coho move northward throughout the spring and appear to concentrate in the central Gulf of Alaska in June.
They later disperse toward shore and migrate along the shoreline until they reach their stream of origin. Although most coho do not seem to migrate extensively, tagged individuals have been recovered up to 1,200 miles from the tagging site.