At three to four years of age, coho salmon reach sexual maturity. From September to October, coho swim to the fresh water streams where they were born (up to 400 miles). Once the fish reach their natal site females dig a nest in a gravel-type area. After the nest is made a female and one male (occasionally 2) breed. In this breeding, the female lays her eggs and the male's sperm is spread over them, thus fertilizing them. After fertilization has occurred, the eggs are buried by other female coho that are digging their nests. Following reproduction, males and females die, giving the waters more nutrients. Larvae hatch 6-8 weeks after fertilization. The larvae remain in the gravel for 2-3 weeks. Coho live in streams or rivers for about a year until they move to the ocean. (Wheeler, 1985)
Average age at sexual or reproductive maturity (male)
Sex: male: 1095 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 1095 days.