Steelhead Trout

Scientific Name: Oncorhynchus mykiss

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Steelhead trout are native to coastal watershed systems from Alaska to Baja California. In California they are the most widely distributed native trout and are found from the western slopes of the Sierra Nevada through the Central Valley to the San Francisco and Monterey Bay.

Steelhead trout and rainbow trout are the same species: Oncorhynchus mykiss. Both are born in freshwater, but steelhead are anadromous.They spend the adult portion of their lives in saltwater, while rainbow trout remain in freshwater their entire lives.

Ocean-going steelhead take on a silvery color, for which they’re named, to blend into their open water environment. When they enter freshwater the silvery color of the steelhead changes to more closely resembled the green, white, yellow and dark spotted river camouflage of their resident rainbow trout relatives.

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Male and female steelhead migrate together upstream to spawn, sometimes to the place where they were born. Some steelhead are known to migrate at least 500 miles to find their ideal spawning grounds! Human impacts on watersheds like dams and development of riparian land make the journey upstream difficult or impossible for many steelhead.

Every year, steelhead spawn December through April. Spawning females use their tail to dig a shallow ditch in a bed of gravel known as a redd. On average, 550 to 1,300 eggs are deposited per redd  and up to 4,000! After depositing her eggs, one or more males fertilizes them. The female then “digs”  upstream of the eggs in clean gravel, burying them in a thin layer.

Steelhead eggs typically take around 30 days to hatch, depending on water temperature. The alevin or “sac fry” will remain in the redd protected by the gravel surrounding them for 4 to 6 weeks, comsuming the yolk sac they are born with and then feeding on plankton. During this long developmental period these eggs and young fish are vulnerable to predation. Fewer than one percent of the newly hatched fry survive their first year. Human impacts on habitat and water quality make life more difficult for the steelhead trout, lowering their already low chances of survival.

As they grow the juvenile steelhead develop a greenish coloration and bars. At this stage the juvenile fish are now called parr, named after these marks on their sides. The parr live in freshwater 1 to 3 years before migrating to sea.

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Before entering the open ocean steelhead go through a process called smoltification. During this process their color and physiology changes so that they are adapted to a life in salt water. Once they have completed this metamorphosis the adult steelhead enter the ocean, where they may live for 2 to 3 years before returning to spawn.

Steelhead are an excellent indicator species for water quality. An indicator species is a species that, depending on how successful it is in an environment, tells us something about the quality of that habitat or ecosystem overall. If steelhead are dying out it is a bad sign for the many species that rely on the watershed to survive, including us.

In 1997 the United States Government listed steelhead as a threatened species under the Endangered Species Act. Today steelhead are threatened or endangered throughout most of the California Coast, and the California Department of Fish and Wildlife estimates 45% of all steelhead statewide will die out in the next 50 years.

As of 1975 the Salinas River still supported a winter run of steelhead that would spawn in the headwaters of the Arroyo Seco and of the Santa Margarita and Tassajara Creeks. Current levels of agricultural and industrial pollution, along with habitat loss and degradation along the main stem of the Salinas and at spawning sites, have made it much harder for steelhead to migrate up the Salinas River.

The Carmel River is one of the last viable steelhead runs along the entire South-Central Coast and has historically been home to a winter run of up to 20,000 steelhead. During the 2012-17 drought less than 500 steelhead were observed to run upstream to spawn.

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