Species
Dworshak National Fish Hatchery is the largest combination producer of steelhead trout and spring Chinook salmon in the world. The hatchery is located in north-central Idaho at the confluence of the North Fork and the main Clearwater River, just below Dworshak Dam. The dam blocked migrating steelhead from natural spawning grounds on the North Fork of the Clearwater River. Dworshak National Fish Hatchery is unique in that water temperatures for steelhead rearing ponds can be controlled through recirculation similar to an aquarium. This system enables the hatchery to recycle up to 90% of the used water, heated to 54˚ F in the winter, allowing juvenile steelhead to be released in just one year at a length of 8 inches. Fish hatched in the river would take an additional year to reach the same size in the much colder water temperatures. Salmon are raised in 38 F water for 18 months and are released each spring. The famous Clearwater “B” strain of steelhead trout return to the hatchery from the Pacific Ocean, more than 500 miles away, from October until May, and are spawned from January through April. Chinook salmon return from May to August, and are spawned from late August to early September. Returning adult fish swim up the hatchery fish ladder directly into large holding ponds. These fish are three to five years in age and weigh from 12 to 20 pounds, much less than when they left the ocean several months earlier. Eggs are collected from ripe adult females and mixed with milt collected from males to complete fertilization. Fertilized eggs are placed in incubation trays until they reach the ‘eyed’ stage, when black eyespots are visible. The eggs are sorted, counted and moved to special hatching jars in the larger nursery tanks. Steelhead and salmon hatch with yolk sacs attached, which provides their only source of food for the first few weeks of life. Once the yolk sac is absorbed, the young fish are fed a finely powdered fish food several times daily. The young fish remain in the nursery tanks for several months until they reach the ‘fry’ stage, then are moved to outside rearing ponds. All steelhead and most Chinook fry receive some type of fin-clip or other identifying mark by means of an automated marking trailer onsite. The clips, marks or tags indicate these fish were raised in a hatchery. Each Spring, as the fish begin to smolt (an internal change preparing them for life in saltwater) half of the fish are released directly from the hatchery rearing ponds into the Clearwater River, and the rest are trucked to upstream tributaries to begin their downstream migration. To aid the juvenile fish in this journey, eight dams on the lower Snake and Columbia Rivers increase their water releases during the summer months to help push the fish downstream more quickly. Salmon and steelhead can also be collected at the dams and barged or trucked downstream beyond Bonneville, the first dam on the lower Columbia River. In an ideal year, 6,500 eggs from one female steelhead could produce up to 55 adult fish back to the Clearwater River in three years. For Chinook salmon an average of 3,000 eggs per female will yield approximately 2 adult fish returning to the river in three years. |
