What’s the difference between a rainbow trout and a steelhead? With the opening of trout season on the Lower Yuba River, we’ve asked SYRCL’s fish biologist Tyler Goodearly to educate us.
My name is Tyler Goodearly and I am SYRCL’s fish biologist. You can read more about me here. I recently started sharing fun fish facts about some of the native fish who inhabit the beautiful waters of the Yuba.
Rarely is it the case that the Latin name makes it easier to discuss a species than the common name. Except in reference to Oncorhynchus mykiss, better known as rainbow trout or steelhead. O. mykiss are the most widespread, native salmonid in the western North America. It has also been introduced throughout the world including coldwater streams in South and Central America, Africa, Asia, Europe, New Zealand, Australia, Papua New Guinea, Tasmania, and Hawaii.
The key to O. mykiss’s success is its flexible life history pattern that allows an individual to stay in the river its entire life, or migrate to the ocean and return to river habitats to spawn, known as a steelhead. If an O. mykiss spends its entire life in a single river it is known as a rainbow trout.
But, if an O. mykiss travels to the ocean before returning to a river to spawn it’s called a steelhead. It has been observed that offspring of resident rainbow trout sometimes become steelhead and that the offspring of steelhead sometimes become resident rainbow trout. This beautifully complex strategy continues to baffle scientists who want to know why some choose to stay and others choose to migrate.
The Lower Yuba River is home to the subspecies Oncorhynchus mykiss irideus’s Evolutionarily Significant Unit (ESU) the Central Valley steelhead (federally-listed as threatened) and its resident counterpart.
For more information on what SYRCL is doing to help Central Valley steelhead in the Yuba River, check out our restoration projects and the Yuba Salmon Now campaign.
Figure 2: Fish biologist Aimee Taylor boasts a steelhead caught and released on the Klamath River. Photo taken by Matt Drummond.
Name: Central Valley Steelhead
Scientific name: Oncorhynchus mykiss irideus
Other names: Anadromous rainbow trout
Resident Rainbow Trout Diet: aquatic organisms drifting and suspended in the water column, terrestrial insects, and benthic macroinvertebrates.
Steelhead Diet: When in marine environments, steelhead feed on krill and, as they get bigger, small fish and squid.
Status: Central Valley steelhead were listed as federally threatened by NMFS in 1998.
Historic numbers: Pre-colonialism, it is estimated that 50,000 to 100,000 adult steelhead would return to the Sacramento-San Joaquin River System annually. At one time, the Lower Yuba River supported the largest, naturally-reproducing Central Valley steelhead population.
Current numbers: According to a 2016 study by NMFS, an average of only 4,600 Central Valley steelhead return annually to spawn. Of these, an average of 217 return to the Lower Yuba River annually (preliminary data).
Biggest threats: Impassable dams that block access to historic spawning habitat, water diversions, introduced species, water pollution, disruption of gravel supply, interbreeding between hatchery and natural-origin fish, and lasting effects of the Gold Rush.