This Idaho Steelhead article is reprinted from the Idaho Fish and Game website
Idaho Steelhead Species Profile
Steelhead are a native type of rainbow trout that are anadromous. Anadromous means they spawn in freshwater streams, go to the ocean to grow, and return to fresh water as adults. They are common to the Clearwater, Snake and Salmon Rivers.
Idaho’s A-run steelhead are most commonly found in the Snake and Salmon rivers. Their return from the ocean usually starts between June and August and most often they return after spending one year in the ocean. A-run steelhead weigh 4 to 6 pounds and are generally 23 to 26 inches in length.
The B-run steelhead most often return to the Clearwater River, but some return to tributaries in the Salmon River. These fish usually spend two years in the ocean, and start their migration to Idaho later in the summer or fall of the year; usually in late August or September. Because of the extra year and the extra summer of growing in the ocean, they return as much bigger fish.
Average B-run steelhead weigh between 10 and 13 pounds and are 31 to 34 inches long. Steelhead grow very large when they spend a third year in the ocean before they return to Idaho to spawn. These steelhead are usually larger than 37 inches and often weigh more than 20 pounds. The Idaho state record steelhead was 30 pounds and was caught in the Clearwater River in 1973.
Idaho Steelhead Life History
Steelhead spawn in streams from mid-April to late June. They use areas of gravel, or cobble, depending on the size of the fish. The female selects a place in a riffle area below a pool to dig a redd (nest). She displaces the gravel with her body and tail, and the male fertilizes the eggs as they are deposited. The female covers the eggs with gravel by continuing upstream and the current carries the gravel over the eggs.
The eggs hatch in early to midsummer. The young fish live in the stream and migrate to the ocean, usually after two years of rearing in the stream. The juvenile fish that migrate to the ocean will grow rapidly.
When they mature and are ready to spawn, the steelhead migrate back to the place they were born. They enter the lower river drainages in the fall (Sept.-Oct.) and winter over to spawn the following spring, which allows a fall and spring fishing season.Most require 3 to 5 years to mature.
Steelhead trout eat insects and zooplankton in the water or on the surface. They will also feed on small fish and fish eggs. As they get larger, they will eat larger fish. Adult steelhead holding in the river prior to spawning do not eat much, but will strike at food or lures.