Steelhead, Oncorhynchus mykiss
Identifying characteristics: (Non-Native Fish) Two dorsal fins including one adipose fin, mouth and gums are light, small spots along rays on entire tail, 10-12 rays in anal fin.
Steelhead is a name given to migratory rainbow trout that are born in rivers but spend most of their lives in the ocean or the Great Lakes. They eventually return to spawn in the river in which they were born. Rainbow trout are native to North American waters west of the Rocky Mountains. Steelhead runs occur in many west coast streams from northern California to Alaska. They are a popular game fish, and for this reason have been introduced all over the United States.
Great Lakes Steelhead are highly migratory, roaming large areas of the open lakes. They are usually found within 50 feet of the surface, even when over waters that are hundreds of feet deep. They prefer water temperatures of 58-62 degrees Fahrenheit. In the spring and fall, they are often found in the shallows near stream outlets. During the lake-dwelling part of their life cycle, they primarily feed on baitfish like Alewives or Rainbow Smelt, although at times they will feed on insects and other aquatic life. Although they feed primarily in mid-depths, they do occasionally take surface insects. In early summer, they can often be found near the surface among thermal bars of mixing water temperatures. These areas, called "scumlines", attract insects and baitfish, which then attract the Steelhead. Great Lakes Steelhead enter their spawning streams from late October to early May. Although many Steelhead enter the rivers in the fall and overwinter there, spawning does not occur until spring. The fall-run fish are typically the first to spawn, often in March, followed by the spring run fish in April. Spawning takes place in a bed of fine gravel, usually in a riffle above a pool. Steelhead don't necessarily die after spawning; they may live to reproduce several times. Most rainbow trout return home to spawn in the stream in which they were born or stocked.
Steelhead eggs hatch in four to seven weeks, depending on water temperature. Young Steelhead need to grow to approximately 8 inches before they migrate or "smolt" out to the big lake. In most streams, this takes two years. In conditions of good growth, they may reach smolting size in one year, but in sterile conditions they may stay in the stream for up to three years. Most Great Lakes Steelhead reach sexual maturity after spending 2 to 3 years in the lake. While adult Great Lakes Steelhead can reach 36 inches in length and up to 20 pounds in weight, the average adult size for Steelhead is 6 to 7 pounds. Life expectancy for Great Lakes Steelhead is four to six years.
During the stream-dwelling phase of their life cycle, larger fish, fish-eating birds and mammals are the Steelhead's natural enemies. During the open water phase of their life cycle, Sea Lamprey and humans are their primary predators.
Steelhead are valiant fighters, making them a very popular species for sport fishing. They are pursued by Great Lakes trollers, pier anglers and surf anglers. They also provide an exciting river fishery in many Great Lakes tributary streams. Steelhead make great table fare and their fillets can be smoked, grilled, broiled or fried. This is an unbeatable combination that makes them one of Michigan's most popular sport fish!
Steelhead graphic courtesy of Joseph R. Tomelleri and copyrighted.