Onchorhynchus mykiss, (Walbaum, 1792
Steelhead, the anadromous form of rainbow trout, are economically important as a commercial fishery and culturally important to Native American Tribes. Steelhead are one of the top five recreational fish species in North America. Steelhead have been known to jump 11ft (3.35 m) into the air when climbing falls on migration runs and can go from zero to 25 mph (40.2 kmsec) in one second! The offspring of two steelhead parents may become a purely fresh water form of rainbow trout and the offspring of two freshwater resident forms of rainbow trout might evolve into the anadromous form of rainbow trout called “steelhead”. The oldest steelhead ever captured was 11 years of age. 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. Rainbow trout can normally weigh between 8 – 11 lbs. (3.6 – 5 kg). There have been reports of steelhead weighing up to 55 lbs. (25 kg).
SIZE: Steelhead normally reach lengths of 24 in (61 cm) but have been reported reaching lengths of 45 in (120 cm).
RANGE: Historically, rainbow trout or steelhead are native to North America, west of the Rocky Mountains.
HABITAT: Depending on what phase of their life history strategy they are in, steelhead live in freshwater rivers and streams, estuaries and marine environments. Steelhead occupy freshwater streams or lakes during spawning and then migrate back through brackish water to the open ocean to live during their adult non-spawning phase of their life cycle. Steelhead spend most of the year in estuaries or open ocean and only return to fresh water to spawn.
DIET: Steelhead feed on a variety of aquatic and terrestrial invertebrates and small fish. They normally feed on zooplankton when they are young and as they mature begin to include fish eggs, crustaceans, mollusks, small fish and even mice in their diet.
Rainbow trout that exhibit an anadromous life history strategy are commonly referred to as “Steelhead.” Many anadromous populations of steelhead exhibit a distinct shape difference from their freshwater siblings. In many cases steelhead have a pronounced, streamlined, hydrodynamic body shape. In general, steelhead are typically larger than rainbow trout because they spend two to three years in freshwater followed by two to three years in saltwater. Unlike their salmon cousins, steelhead are multiple spawners.
Steelhead can be divided into two basic reproductive types based on their sexual maturity during their spawning migration. These two reproductive types are named “stream maturing” and “ocean maturing.” Steelhead can be grouped into winter or summer runs, depending on when the adults return to fresh water to spawn.
Male steelhead mature at two years and females at three years. Juvenile steelhead may spend up to seven years in freshwater before migrating to brackish waters and then into the ocean where they begin to mature. These fish can then remain at sea for up to another 3 years before returning to fresh water to spawn.
Some steelhead populations will actually return to freshwater after their first season at sea but will not spawn. They will then return to the ocean after one winter season in fresh water.
Steelhead are very susceptible to human induced changes within their habitat. Native populations of steelhead are threatened by habitat degradation, fishing pressure and diseases such as “whirling disease,” a parasitic disease that can cause skeletal deformities and death in young steelhead. Unfortunately, steelhead are also very susceptible to hybridizing with other trout which might include non-native species.
The National Marine Fisheries Service (NMFS) has designated 12 distinct population segments of steelhead on the west coast of the United States. The steelhead form of rainbow trout has one distinct Endangered species population segment, ten distinct Threatened species population segments, and one distinct Species of Concern population segment listed under the Endangered Species Act.
The National Fish Hatchery System of the U.S. Fish and Wildlife Service raises over six million steelhead each year for recreational fishing, commercial fishing, tribal or subsistence harvests and to help recover threatened steelhead populations.