Where Steelhead Meet Science

The warm sun shone brilliantly through the canyon pool, casting shadows around summer-run steelhead haphazardly cruising about. These black shapes dotted the canyon, like stealthy submarines lying in wait.

Since I already had one from the first run of the day, my two companions fished adamantly for them, taking turns casting streamers and dries, but with a few refusals and a missed hookup, we eventually decided to break for lunch.

We shared hummus and pita bread, and while the other two were occupied with conversation, I scaled a small bluff, pulling myself up by any foot- or handhold I could manage. From above I saw two fish. One seemed to be in a trancelike state, while the other slowly cruised around the pool. I went back and asked Francco to pass my rod. He strained to extend the rod high enough until I was just able to grab the tip and pull it up. I walked back over to the other side to see that the cruising fish had slowed down and stopped. I stripped line from my reel into a puddle at my feet and made a decent cast, my dry fly landing about a metre in front of the fish with a slight ripple. I stripped it twice and it gave one quick pulse of its tail but then lost interest. “It went for it,” I said in awe—whether to myself or my friends, I can’t recall.

I gently stripped the fly towards me and presented a similar cast. Within two strips the steelhead engulfed my dry fly.

I lifted the rod in disbelief and felt the immovable weight of a rather large summer-run. It leapt through the pool and took darting runs, perturbed by its invisible tether, until finally it came close enough for Francco to scoop the net under it. I climbed back down the bluff and gazed at the fish. “What has it seen?” I wondered as my fly slid out of the semi-docile fish’s mouth. It journeyed up nearly 20 km of river, but its life history reflected millennia of steelhead evolution.

What is a Steelhead?

Steelhead lead an incredible life— especially as they have the ability to adjust to saltwater environments—but first let’s cover some simple facts. Commonly mislabeled “steelhead salmon,” they are simply the sea-run version of rainbow trout; in fact, both steelhead and rainbows share the same scientific name, Oncorhynchus mykiss. When they spawn, they migrate by their sense of smell to their home rivers, after 1 to 4 years in the ocean (in April to October for summer-run and November to May for winter-run). Similar to rainbow trout, they spawn in oxygenated gravel beds in the spring from around late April to May. While the parents attempt their return to the ocean, their offspring hatch from eggs into parr and then either become rainbow trout or steelhead smolts. Smolts will then make their way towards the ocean, spurred on by the lengthening spring days. From there they will travel the North Pacific, feeding on baitfish, squid, and shrimp.

Is it a Steelhead or Rainbow Trout?

The recent removal of the Elwha Dam in Washington State allowed rainbow trout trapped above the dam to migrate to the sea, creating a new run of summer steelhead. According to Neala Kendall, a steelhead scientist, individual parr will conform either to saltwater or freshwater life based on their status as juveniles. Their size, stored fat, age, and genetics dictate their tendency to migrate to the oceans. If there is plenty of food or other favorable conditions, they may remain in freshwater. If they do choose to pursue ocean migration, juvenile steelhead undergo a process called “smoltification” where they make physiological changes for saltwater adaptation.

According to John R. McMillan, science director at The Conservation Angler, “juvenile steelheads that become smolts lose their drab appearance and become silver, often with black-leading edges on their fins. Their body becomes more fusiform [slender and elongated] and their scales become loose, [and then] the fish will begin migrating to the ocean. This process is then reversed once the fish starts to mature and needs to re-enter freshwater to spawn.” The likelihood of a steelhead surviving ocean migration is incredibly rare. Historically it varied at 10–20% but now hovers at 1–2% depending on the region.

What is Anadromy?

Steelhead and salmon are classified as anadromous fish since they can tolerate both freshwater and saltwater environments. While we might think these environments are somewhat similar, the addition of salt creates a vastly different environment for fish to live in. As with many organisms on the planet, salt is an important component for a fish’s body. In salt-deficient environments, bodily processes of freshwater fish uptake salt, while saltwater fish undergo a process that actively removes a majority of salt. Maintaining the physiological balance is called smoregulation. The ability to switch between these processes requires different enzymes and kidney functions, but anadromous fish like steelhead and salmon can miraculously alter their enzymes and kidneys to switch from salt excretion to sequestration. This physiological mechanism allows for the rapid (re)colonization into rivers and streams, perhaps after the retreat of a glacier and the benefits of a food-rich ocean environment.

Summer v.s. Winter-Run Steelhead

Scientific literature doesn’t identify an advantage for summer- over winter-run timings (or vice-versa), but summer-run steelhead need more time to make their migration than winter-runs. Both winter- and summer-runs spawn at the same time but are separated by geographical barriers. Summer-run steelhead tend to colonize the upper reaches of river systems; therefore, to make this long journey, they sexually mature after entering the river; conversely, winter- run steelhead can spawn within days of entering the river. To paraphrase a metaphor from John McMillan: Summer-run steelhead show up to the party early, before the beer is out and the music is flowing, while winter-runs show up just as the party is at its peak. Genetically, however, summer and winter steelhead are nearly identical except for one gene. This mutated, protein-coding gene, GREB1L, has given rise to summer-run steelhead, which appear to have evolved over 15 million years ago, and if lost, may never occur again. This promotes the idea that summer-run steelhead are their own Evolutionarily Significant Unit, which, in the context of conservation, means that specific protections must be placed on these different run-timings of steelhead.

Steelhead Preservation: A Necessary Discussion

A steelhead article would be remiss without a section on preservation. According to the Wild Steelhead Coalition, there are five main threats to wild steelhead: habitat, heat, harvesting, hatcheries, and hydropower. Steelhead are becoming increasingly threatened, so we anglers we must do what we can. Reach out to MLAs and advocate for better steelhead protections, donate to organizations that help mitigate threats to steelhead, and make sure to practice ethical catch-and-release methods. We all want the next generation to experience the same thrills and adventures we have had: exploring rivers and descending canyons, bushwhacking through dense thickets, and enduring winter’s oppressive cold in pursuit of this unique fish.

This article appeared in Island Fisherman magazine. Never miss another issue—subscribe today!