Habitat Type: Freshwater
Comments: Coho salmon usually spend 2 (range 1-3) growing seasons in the ocean before spawning. In the ocean, they remain over the continental shelf and generally stay within 30 km of their natal stream (but some may range up to several hundred kilometers away).
Spawning occurs in just about any accessible coastal stream, generally in forested areas, usually at 6-12 C in loose coarse gravel at heads of riffles (or tails of pools) in rounded troughs excavated by females where water is 10-54 cm deep. Females construct and deposit eggs in each of several redds. Individuals generally spawn in their natal stream; however, rapid colonization of newly accessible habitat has been observed.
Young spend a few weeks to 2 years (varies geographically) in freshwater streams before migrating to the sea (young in the north spend a longer time in fresh water than do those in the south). Often this period is substantial and amounts to approximately half of the life cycle. Hatchlings that have left the spawning site seek shallow water, usually along stream margins. Older juveniles prefer pools and runs with good cover, high oxygen levels, and abundant invertebrate populations. Fry may summer in brackish water in southeastern Alaska.
Stocked populations in lakes and reservoirs migrate upstream to spawn or more commonly do not reproduce (must be restocked annually).