The Superpowers of Steelhead: Nature’s Shape-Shifter

Did you ever dream about having superpowers as a kid? What was your favorite? Invisibility, flying, teleportation?

Sadly, and despite great longing, I’ve never been able to fly. No bump on the head, no superpowers.

As a scientist, however, I’ve come to appreciate that we all have unique strengths and abilities. Salmonids are the same. For example, Chinook are massive in size and strong enough to move boulders and spawn in the largest rivers, while coho are explorers that push into the smallest streams.

But what if you could be the shapeshifter with all the superpowers?

That is basically the case with steelhead and rainbow trout, collectively O. mykiss. They take multiple forms, from freshwater residents in small streams to long distance elite endurance athletes that ascend and spawn in large streams.

Steelhead are found from Baja California around the Pacific Rim to the Kamchatka Peninsula in Russia, from high-elevation desert streams, through cold coastal rainforests, to treeless tundra. This range is no accident. It’s the result of their incredible biological flexibility, a suite of traits that have allowed them to thrive in wildly different environments.

That’s their real superpower. Flexibility to take on whatever form best fits their surroundings.

Steelhead epitomize the saying “don’t put all your eggs in one basket.” They can dig more than one redd, spawn from November through July, and spend 1-4 years in freshwater before migrating to sea. Some may remain in freshwater as residents, while others may literally shapeshift between anadromy and residency.

Not only can steelhead choose whether to migrate to the ocean or not, they can spawn, return to the ocean and spawn again in future years. This flexibility is a biological insurance policy that increases resilience, such as when seaward migration is blocked or when marine survival is poor.

From riffles to pools and headwater tributaries to mainstem rivers, steelhead use more types of habitat than perhaps any other salmonid. Their swimming and leaping ability, which is unmatched among Pacific salmonids, allows them to pass barriers and reach habitats others cannot. They will ultimately spawn in coastal rivers near tidewater, high elevation rivers 1,000 miles inland, and everything in between. Spawning adults and their juveniles occupy every nook and cranny of a watershed. They are neighbors with all salmonids, from chum salmon in lower mainstems to cutthroat trout and coho salmon in the smallest streams.

This ability to use, and thrive in, so many habitats makes Mykiss remarkably adaptable. But it also complicates management. To support steelhead, we have to think not only about the diversity that allows them to occupy such a wide range of habitats, but we have to ensure there are enough spawning adults to spread their juveniles across a watershed, otherwise some areas may be underutilized.

Steelhead don’t just distribute more broadly in space, they also do so in time. Unlike other salmon species that return and spawn in a relatively narrow seasonal window, steelhead enter freshwater every month of the year, even in a single watershed. Some return in spring and summer and hold for months before spawning, while others return sexually mature, or nearly so, shortly before spawning. This variability spreads risk and buffers against poor conditions in any single season. It also means we, as anglers, can pursue our favorite fish almost anytime the desire strikes us.

This incredible range of habitat use across space and time means that steelhead must cope with widely varying temperature regimes, from anchor ice in winter to soaring summer temperatures that would kill many of their salmon cousins. Undoubtably, steelhead have an incredible thermal tolerance, but they also have flexibility in the age at which they migrate to the ocean. In colder regions parr grow in summer, while in warm areas they may grow more rapidly in winter. If they live in the Goldilocks zone, they may grow year-round. Their biological programming is more flexible than salmon. Whether that means growing fast and migrating to the ocean as a 1-year-old, or growing only during short cool summers and migrating to the ocean as a 4-year-old. Hence, while salmon stick to their scripts, steelhead adapt and improvise to get the job done.

Climate change is no longer a distant threat, it’s happening now. Lower and warmer summer flows have become evident in our favorite rivers and backyard streams. Fortunately for steelhead anglers, Mykiss have already demonstrated they can adapt to massive climate shifts. They recolonized entire regions as ice ages ebbed and waned, adjusting to dramatic climate shifts with sea levels rising and falling over 100 meters. But today’s changes are occurring at a very rapid rate, and the earth appears poised to enter into conditions not experienced for millions of years.

The timing of life events will need to shift to match the changing seasons, with spawning, emergence and smolting happening earlier in the year. This is where the ability to shapeshift gives steelhead a leg up on their salmon counterparts. Mykiss don’t need to evolve new traits in the near term, instead they will draw upon their existing deep pool of genetic and life history diversity to adapt.

The inherent diversity of Mykiss makes them resilient but doesn’t mean they’re invincible. In fact, steelhead continue to decline across much of their range. But with the right protection, allowing for full expression of life histories, steelhead have a fighting chance at recovery and persistence.

Unfortunately, modern management often fails to recognize or support these traits. Hatchery programs whittle away at diversity. Harvest does the same. Monitoring practices often ignore the range of timing and extent of habitat use, leading to incorrect assumptions about limiting factors. And managers rarely consider maintenance of diversity in structuring fisheries.

Understanding the superpowers of steelhead isn’t just a scientific curiosity, it’s a management imperative. If we want to conserve wild steelhead, we have to embrace their complexity, not simplify it. That means protecting diverse habitats, supporting full life history expression, and allowing natural selection to operate within and among populations.

These traits are also what make steelhead special to me and why so many anglers pursue them. Whether it is large ocean fresh fish in winter, dry flies and wet wading in summer, or simply observing the annual cycle through a snorkel mask, every month of the year brings something unique. I am hopeful for the future of these fish, if we can get out of their way and nurture their flexibility, rather than hinder it.

In the coming months, we’ll be diving deeper into each of these topics. We'll look at how steelhead can adapt to climate change and where they may struggle the most, and why the way we manage fisheries will be key to their survival. Most importantly, we’ll explore what it means to manage steelhead according to their unique biology.