Steelhead and Coho Salmon Life Cycle
Steelhead and coho salmon are anadromous fish –they spawn in freshwater and mature in the ocean. Steelhead that never enter the ocean and remain in freshwater streams are called rainbow trout.
Adult steelhead migrate upstream from the ocean during the rainy season, anytime from November to March. Steelhead and coho salmon enter local streams only when sufficient streamflow has opened coastal lagoons through which the stream drains to the ocean. Steelhead spawn (mate and lay eggs) typically at the downstream edge of pools where cover habitat exists nearby for predator protection. Eggs are laid in a depression dug into cobble or gravel substrate called a redd. Unlike salmon, steelhead can migrate out to the ocean after spawning and return in subsequent years to spawn again. Eggs hatch in 30-60 days, depending on stream temperatures. The newly hatched fish – called alevins – stay in the gravel for a few additional weeks, until their yolk sac is absorbed. When they emerge, they seek slow-water areas, often at the stream margins. As they grow bigger, the young fish – called juveniles – move into faster water to feed on drifting insects.
Juvenile steelhead remain in freshwater streams from 1 to 3 years, depending on their rate of growth. Rearing juveniles have many habitat requirements. Most important, they need sufficient, cool streamflow to transport drifting insects for feeding, and cover habitat such as undercut banks, woody material, boulders and deep pools to hide from predators and have refuge during high flows. When juveniles are large enough, they migrate out to the ocean as smolts. During this out migration, steelhead and salmon need adequate streamflow to swim past barriers, and cover for predator protection.
Coho salmon have a similar, but more rigid lifecycle than steelhead. Coho salmon spend their first year in freshwater streams, migrate out to sea where they mature for two years, and return to their native creeks to spawn and die. Because all non-hatchery females are three years old, coho salmon develop three consecutive "year classes" in each stream. Coho salmon are at the southern distribution of their range in Santa Cruz County. They are vulnerable to extreme environmental conditions such as droughts, floods, and the timing of winter storms, which affects when the sandbar opens for upstream migration and affects the survival of redds and juveniles.
Coho salmon were listed in 1995 as endangered south of San Francisco down to and including Santa Cruz County under the State Endangered Species Act (ESA). In 1996, the National Marine Fisheries Service listed coho salmon as threatened under the federal ESA from the San Lorenzo River (inclusive) to Mendocino. Steelhead were federally listed as threatened along Central California in 1997. An ESA listing is complex and has large impacts on land use practices, water use, and on the fishery (the California commercial coho fishing was banned in 1993 and recreational fishing was banned in 1994). Sate Fish and Game and the National Marine Resources Service are now working together to develop a watershed management approach to restoring salmonid populations. Local entities are encouraged to begin developing modifications to their own policies and operations to protect and restore habitat, and partially in response to this the County Board of Supervisors adopted in 2001 the County of Santa Cruz Fish Net 4C Implementation Plan identifies the County's highest priority actions for protecting and restoring salmon habitat.
Large climatic cycles affect not only the timing and intensity of winter storms, but also influence the survival and return of adult steelhead and coho salmon. While humans cannot control the weather or natural ocean conditions, we can protect and enhance the freshwater environment where these fish spawn and rear.
Stream Habitat and Juvenile Steelhead Monitoring