Information sources NOAA NMFS and CalFish
Species Description - Steelhead Trout
Weight: up to 55 pounds (25 kg), but usually much smaller
Length: up to 45 inches (120 cm), but usually much smaller
Appearance: dark-olive in color, shading to silvery-white on the underside with a heavily speckled body with a pink-red stripe along their sides; in the ocean, they become more silver
Lifespan: up to 11 years;
sexually mature at 2-3 years
Diet: zooplankton while young;
adults feed on aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes (including other trout)
Behavior: migrate from a marine environment into the freshwater streams and rivers of their birth in order to mate;
females will prepare a "redd" (or nest) in a stream area and may deposit eggs in 4-5 "nesting pockets" within a redd
Steelhead trout can reach up to 55 pounds (25 kg) in weight and 45 inches (120 cm) in length, though average size is much smaller.
They are usually dark-olive in color, shading to silvery-white on the underside with a heavily speckled body and a pink to red stripe running along their sides.
They are a unique species; individuals develop differently depending on their environment. While all O. mykiss hatch in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams, some stay in fresh water all their lives. These fish are called rainbow trout. The steelhead that migrate to the ocean develop a slimmer profile, become more silvery in color, and typically grow much larger than the rainbow trout that remain in fresh water.
Adults migrate from a marine environment into the freshwater streams and rivers of their birth in order to mate (called anadromy). Unlike other Pacific salmonids, they can spawn more than one time (called iteroparity). Migrations can be hundreds of miles.
Young animals feed primarily on zooplankton. Adults feed on aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes (including other trout).
Maximum age is about 11 years. Males mature generally at 2 years and females at 3 years. Juvenile steelhead may spend up to 7 years in freshwater before migrating to estuarine areas as smolts and then into the ocean to feed and mature. They can then remain at sea for up to 3 years before returning to freshwater to spawn. Some populations actually return to freshwater after their first season in the ocean, but do not spawn, and then return to the sea after one winter season in freshwater. Timing of return to the ocean can vary, and even within a stream system there can be different seasonal runs.
Steelhead can be divided into two basic reproductive types, based on the state of sexual maturity at the time of river entry and duration of spawning migration:
The stream-maturing type (summer-run steelhead in the Pacific Northwest and northern California) enters freshwater in a sexually immature condition between May and October and requires several months to mature and spawn.
The ocean-maturing type (winter-run steelhead in the Pacific Northwest and northern California) enters freshwater between November and April, with well-developed gonads, and spawns shortly thereafter. Coastal streams are dominated by winter-run steelhead, whereas inland steelhead of the Columbia River basin are almost exclusively summer-run steelhead.
Adult female steelhead will prepare a redd (or nest) in a stream area with suitable gravel type composition, water depth, and velocity. The adult female may deposit eggs in 4 to 5 "nesting pockets" within a single redd. The eggs hatch in 3 to 4 weeks.
Steelhead are capable of surviving in a wide range of temperature conditions. They do best where dissolved oxygen concentration is at least 7 parts per million. In streams, deep low-velocity pools are important wintering habitats. Spawning habitat consists of gravel substrates free of excessive silt.
It has been reported that 7 inches is the minimum depth required for successful migration of adult steelhead although the distance fish must travel through shallow water areas is also a critical factor. Excessive water velocity and obstacles which impede the swimming and jumping ability are significant in hindering or blocking migration. Water velocities of 10 to 13 ft/s begin to hinder the swimming ability of adult steelhead and may delay migration. Optimum temperature requirements vary based on stock but generally fall in the range of 46 to 52°F.
The preferred depth for spawning ranges from 6 to 24 inches with an average of 14 inches. Steelhead spawn in areas with water velocities ranging from 1 to 3.6 ft/s but prefer velocities of about 2 ft/s. Larger steelhead have the ability to establish redds and spawn in faster currents than smaller steelhead.
Adult steelhead have been reported to spawn in substrates from 0.2 to 4.0 inches in diameter. Based on the Bovee (1978) classification, steelhead utilize mostly gravel-sized material for spawning but will also use mixtures of sand-gravel and gravel-cobble.
Optimum temperature requirements vary based on stock but generally fall in the range of 39 to 52°F.
Eggs and sac fry in the gravels interstitial spaces require highly permeable gravels to keep the incubating eggs and sac fry well oxygenated and should contain less than 5% sand and silt. Once fry emerge from the gravel, they utilize water in the range of 2 to 14 inches in depth and prefer water approximately 8 inches in depth. Fry prefer substrate categorized as cobble/rubble which is slightly larger than that preferred by adult steelhead for spawning. Optimum temperature requirements vary based on stock but generally fall in the range of 45 to 60°F.
Parr prefer a water depth of 10 inches but utilize water 10 to 20 inches deep. Juveniles prefer substrate categorized as cobble/rubble which is slightly larger than that preferred by adult steelhead for spawning.
Optimum temperature requirements vary based on stock but are generally less than 57°F.
In the United States, steelhead trout are found along the entire Pacific Coast. Worldwide, steelhead are naturally found in the Western Pacific south through the Kamchatka peninsula. They have been introduced worldwide.