Coho salmon (Oncorhynchus kisutch) are a Pacific salmon species, often called “silver salmon” due to their bright, metallic sheen. These anadromous fish migrate between freshwater and saltwater environments. Their life cycle involves hatching in freshwater streams, spending time in the ocean, and returning to their birth streams to reproduce. This migratory behavior and specific habitat requirements make them a significant part of North Pacific ecosystems.
Key Identification Features
Coho salmon’s appearance changes with their life stages. In their ocean phase, they have a dark metallic blue or greenish back, silver sides, and a light belly. They also have small black spots on their back and the upper lobe of their tail fin. Their lower jaw’s gumline is typically lighter than other salmon species like Chinook.
Upon returning to freshwater for spawning, their appearance transforms. Their bodies darken, developing reddish-maroon coloration on their sides. Spawning males grow a strongly hooked snout, called a kype, and larger teeth, while females show less vibrant coloration. Juvenile coho, known as parr, have vertical bars and spots that fade as they transition into smolts, gaining the dark back and light belly of ocean-dwelling coho. Adults generally average 24 to 30 inches in length and weigh 8 to 12 pounds, though some can reach up to 42 inches and 36 pounds.
The Coho Life Cycle
The coho salmon life cycle begins in freshwater streams, typically in fall or early winter. Females construct nests called redds in gravel beds, laying 300 to 1,200 eggs. These eggs incubate for six to seven weeks, depending on water temperature, remaining protected until they hatch.
Upon hatching, young coho are alevin, characterized by a yolk sac that provides nourishment. They remain in the gravel until the yolk sac absorbs, then emerge as free-swimming fry. Fry reside in shallow stream margins, feeding on plankton and insects, and develop distinctive parr marks for camouflage. After nine to 16 months in freshwater, typically a year, these juveniles undergo smoltification, preparing them for saltwater.
As smolts, they migrate downstream to estuaries and then to the Pacific Ocean, usually between March and July. In the ocean, coho spend about 18 months, feeding and growing rapidly, often adding over 95% of their adult body weight. Their diet includes small fish like herring, sandlance, anchovies, and sardines, as well as squid and crustaceans. After one to three years at sea, mature coho return to their natal freshwater streams to spawn, typically between ages three and four, and then die.
Habitats and Distribution
Coho salmon use various habitats throughout their life, from small freshwater streams to the North Pacific Ocean. In freshwater, they require cold, clear, well-oxygenated streams with gravel beds for spawning and rearing. These streams often include side channels, floodplains, and areas with woody debris, providing shelter and foraging grounds for juveniles. Coho are adaptable and can inhabit smaller rivers and tributaries that might be too restricted for other salmon species.
As juveniles transition to saltwater, estuaries serve as intermediate habitats before they venture into the open ocean. Their marine distribution spans the North Pacific, from central California northward along the coasts of Oregon, Washington, British Columbia, and Alaska, reaching Point Hope. On the Asian side, their range extends from the Kamchatka Peninsula to northern Japan. While most coho undertake extensive ocean migrations, some remain in coastal waters closer to their natal streams. Coho have also been successfully introduced and established in North America’s Great Lakes region.
Role in Ecosystems and Human Connection
Coho salmon play a significant role in their ecosystems as both predators and prey. In freshwater, young coho consume plankton and aquatic insects. In the ocean, adults prey on small fish, squid, and crustaceans. They are a food source for numerous animals, including otters, seals, marine mammals, birds, and larger fish. Their anadromous life cycle contributes to nutrient cycling; after spawning, their decaying bodies transport marine-derived nutrients from the ocean back into freshwater and riparian ecosystems, enriching the environment for other species.
Coho salmon also hold importance for human societies. For indigenous peoples of the Pacific Northwest and Alaska, salmon, including coho, have been a foundational resource for thousands of years, embedded in their culture, diet, and ceremonies. Salmon provide physical sustenance and cultural identity.
Economically, coho salmon support commercial fisheries, particularly in Alaska, as a significant component of the annual salmon harvest. They are often caught using troll, seine, and gillnet fisheries. Coho are also highly valued in recreational angling, attracting sport fishermen across their range. Management efforts aim to ensure sustainable fisheries for both commercial and recreational harvest. While some coho populations are robust, certain units along the West Coast are listed as threatened or endangered under the Endangered Species Act, requiring ongoing conservation and management.