Steelhead

The freshwater form of the steelhead is the rainbow trout (Oncorhynchus mykiss). The difference between these forms of the species is that steelhead migrate to the ocean and return to freshwater tributaries to spawn, whereas non-anadromous rainbow trout do not leave freshwater. Steelhead are also larger and less colorful than rainbow trout. Steelhead can weigh up to and can reach in length, but are typically much smaller at around . In the wild, they usually live four to six years and spawn multiple times. The body of the steelhead trout is silvery and streamlined with a rounder head. This silver color and round head is what gives the steelhead its name. Human interaction has had considerable consequences on reducing the population of steelhead trout. == Characteristics ==

Steelhead currently support or have historically supported fisheries across Northern California, and thus they hold "economic as well as cultural value" (Moyle, Israel, & Purdy, 2008). Contrary to popular belief, the California Steelhead is a coastal variation of the same species of fish as the Rainbow Trout, Oncorhynchus mykiss; "rainbow trout are the 'landlocked' version, and remain in freshwater throughout their life" (King County, 2016). An ocean-going variety, the Steelhead, or Oncorhynchus mykiss irideus has developed unique adaptive characteristics that distinguish this fish from its common counterpart and have allowed a wider distribution of this species across the Pacific Northwest, including the coastal regions of California. In fact, "coastal rainbow trout is the most widely-distributed native trout form" (CA.gov). Among other necessary biological utilities fulfilled by this species, Steelhead Trout "are also strong indicators of the condition of California's streams; large self-sustaining populations of native salmon and trout are found where streams are in reasonably good condition" (Moyle, Israel, & Purdy, 2008). A chrome underside and olive-grey back reminiscent to that of a steel beam are attributed as the main defining physical characteristic for which the Steelhead is distinguished and earns its namesake. The Steelhead is an ocean-going predatory fish with a typical lifespan of four to six years. Like the common rainbow trout, Steelhead predominantly feast on zooplankton when they are young and then transition to eating fish, some rodents, mollusks, and crustaceans. When these fish enter the open ocean, however, their diet typically consists of squid, crustaceans, and small fish including anchovies, herring, and sardines, though the capacity at which this dietary intake occurs is highly contingent upon the geographical region where Steelhead choose to migrate (Salmon Fishing Now). "Rainbow trout and steelhead represent two divergent ecotypes that are genetically identical but separated by life history strategies" (Heath 2001); the unique biological diversity of the Steelhead Trout from that of the Rainbow Trout is determined through a capacity to migrate to the open ocean. Homing behavior is a unique adaptation of Steelhead Trout that allows the fish to migrate to and from freshwater and saltwater bodies on multiple occasions. Through the process of imprinting, Steelhead Trout deposit a chemical indicator "that is specific to their natal stream" (NRC 1996). Homing behavior Perhaps the most interesting and perplexing characteristic of the Steelhead Trout is its homing behavior and the capacity of this species to accurately detect its primary spawning grounds despite venturing to the open ocean and returning to the same freshwater source on numerous occasions throughout their lives. By recording the concentrations of solutes and the chemical profile of a stream through the biological characteristic of a chemical indicator, steelhead "use the position of the sun and magnetic north to navigate towards spawning grounds " after they have fed in the open ocean for 1–4 whole years (Fulton). Even after traveling hundreds of miles, this chemical imprint allows steelhead to identify their precise hatching grounds upon returning to freshwater. According to "A review of the characteristics, habitat requirements, and ecology of the Anadromous Steelhead Trout" by Fulton, "homing creates genetically different subpopulations that differ by basin, stream, and even location within a stream" (Altukhov 2000). According to a study conducted by Heath & Pollard, "significant genetic variation on the individual, tributary, and watershed level occur between Steelhead Trout populations" as a result of this chemical reliance for breeding practices (Heath, 2001). The author concludes that as a result of such biologically accurate homing characteristics, the Steelhead Trout is "uniquely adapted to its environment"; fish populations "are reasonably isolated from fish that spawn in different areas," and therefore "sub-populations may differ by the timing of runs, size of fish, and even behavior patterns" (Heath, 2001). This also influences genetic relatedness between Steelhead Trout populations; interestingly, the author found that the genetic similarity of regional Steelhead trout populations "is correlated with distance" (Heath, 2001). == Spawning ==

During spawning, the fish will lay their eggs on gravel bottoms of freshwater tributaries. The female digs out a hole called a redd. The preferred depth for steelhead spawning is . She then lays the eggs, and a male fertilizes them. The females will then cover the eggs with the gravel. Depending on the size of the female she may lay up to 9,000 eggs. The female then buries the eggs in a foot of gravel. The eggs remain in the gravel until they hatch. Unlike salmon (which can spawn only once) steelhead may return to the ocean, and come back upstream several times for spawning season. == Atlantic Canada ==

Small numbers of steelhead are present in Atlantic Canada. == Conservation status ==

There have been several conservation programs created since the near extinction of the steelhead in the 1940s. The reduction in population is mainly due to manmade obstructions within river systems. This is usually caused by dams blocking access, or humans changing the river landscape for recreation and access to water. It is estimated that only 500 steelhead trout return to the Southern California watersheds. However, in other areas of the United States, steelhead can be seen as pests because they are an invasive species to the environment. (NOAA). Of these four segments, three are listed as threatened under the Endangered Species Act. The Middle Columbia River (MCR) segment has remained the focus of recent recovery efforts. The MCR segment covers approximately 3,500 square miles of the Columbia Plateau in eastern Oregon and Washington. Within eastern Oregon, recovery efforts focus on the two main tributaries to the Columbia River: The Deschutes River and the John Day River, although the Umatilla and Walla Walla are also included in recovery plans. Primary threats to MCR steelhead populations include hydrosystem operations, habitat alteration, and effects of stray naturally spawning hatchery fish. ==Notes==