Steelhead Trout

Oncorhynchus mykiss

Description: Steelhead trout (anadromous rainbow trout) typically range in weight from 5 to 10 pounds, but can get up to 45 inches in length and weigh up to 30 pounds. Steelhead in the ocean have metallic blueish-green backs and silver sides especially below the lateral line. When sexually mature for spawning, males have aprominent pink to red band on the operculum (gill cover) and at and below the body’s lateral line; females less so. Males usually do not have the prominent hooked kype (lower jaw) seen in male salmon when sexually mature. Sea-run cutthroat, Oncorhynchus clarkii, is an anadromous coastal cutthroat trout closely related to rainbow trout. The red slash under the lower jaw and greater body and tail spotting are the identifying characters for a sea-run cutthroat

In Whatcom County: Steelhead have two patterns for when they return from the ocean to spawn in Whatcom County streams. Most local steelhead are winter run fish meaning they enter freshwater from October through February and spawn in the March through May (unlike salmon which spawn in late summer to early winter depending on the species). Winter run fish are found in Dakota Creek, urban creeks in Bellingham and major tributaries (for example, Bertrand and Fishtrap Creeks) and the three forks (North, Middle and South) of the Nooksack River.  Additionally, summer run steelhead spawn in the Nooksack South Fork and enter the river between June and September remaining in deep pools until spawning in February through April. South Fork summer run fish are a native stock genetically separate from the winter run stock.

Range:  Major steelhead distribution is from northern California, Oregon, Washington and British Columbia to southeast Alaska, Alaska’s Copper River and to the easternmost Aleutian Islands.  In Asia, significant numbers only on the western coast of the Kamchatka Peninsula.

Life History:  Steelhead spend 1 to 3 years in fresh water and 1 to 4 years at sea.  Most common in Oregon and Washington is a 2 freshwater/2 ocean life history. Steelhead juveniles behave much like resident trout. At sea, steelhead are distributed widely over the North Pacific Ocean.  Because they can survive spawning (iteroparous), some return to the ocean to feed and may return to a stream after a year or more to spawn a second time. Sea-run cutthroat do not have extensive ocean migrations and remain coastal and never are as large as steelhead.

Habitat Requirements: As for salmon, good steelhead habitat is found where water remains cool, clean and well-oxygenated and where aquatic and terrestrial insects are abundant. Because young steelhead spend up to 3 years in freshwater, high-quality stream habitat is essential.  Steelhead spawn at sites similar to those used by coho and Chinook salmon – some evidence suggests that competition for spawning habitat is minimized by spring spawning, after the salmon fry have emerged.

Did You Know: In 2007, Puget Sound steelhead, including those in Whatcom County, were listed as “threatened” under the federal Endangered Species Act. Until 1989, rainbow (and steelhead) and cutthroat ( and sea-run) were in the trout genus Salmo.  Steelhead exhibit reproductive “plasticity” when a female steelhead’s progeny may either become anadromous steelhead or some may become resident rainbow trout. Likewise, a female rainbow’s progeny may become either resident rainbow or some may become steelhead. Steelhead is a game fish and is not commercially harvested but is raised in aquaculture for marketing. Steelhead was successfully introduced into the Great Lakes and also as descendants of rainbow trout planted in New Zealand and Chile. As for Chinook and coho juveniles released from a hatchery, the adipose fin of each juvenile steelhead is removed before release. If an adult steelhead, coho or Chinook lacks the adipose fin when caught, then it is hatchery produced. If it has an intact adipose fin, then it was naturally or wild produced.  

Photo credit: Pacific Salmon- Childerhose and Trim - Douglas & McIntyre Vancouver/Toronto