The Steelhead Puzzle: The Complex and Interwoven Impacts on Wild Steelhead Populations

By Guy Fleischer, WSC Science Advisor

Over the eons, steelhead, the anadromous form of Oncorhynchus mykiss, evolved a wide range of life histories to take full advantage of the hydrologic and physical conditions of individual watersheds across their range. Each river system supported wild fish that developed distinct and heritable characteristics with well-tuned strategies uniquely adapted and tailored to the diverse habitats of their home waters. Steelhead display the most life-history diversity of any Pacific salmonid species and it is this diversity, combined with their ability to spawn more than once, that leads to their resilience and fitness as a species.

Generally speaking, steelhead evolved two reproductive strategies: “winter” (ocean-maturing) or “summer” migrating fish (stream-maturing populations that can enter fresh water up to nine months before spawning); some rivers have both or only one. Wild steelhead further specialized, which is why a Skagit winter fish is different from the half-pounders of Northern California and Oregon and both are different from a large B-run fish returning to the Clearwater River in Idaho. Or a system like the Queets River, on Washington’s Olympic Peninsula, might have multiple, overlapping seasonal populations of winter-run fish returning at different times from November through April. This vast diversity and perfect co-evolution with home waters is the key to the success of wild steelhead populations.

Of course, all steelhead are defined by their migration to and from the sea, the fact that they are able to repeat the journey - unlike their salmon cousins - and by their ability to prevail in the greater web of life in the Pacific Ocean.

Today, wild steelhead face a wide variety of interlocking challenges and their numbers are dangerously low throughout much of their native range. Some systems, like the Columbia Basin and the mighty Skeena, saw their worst returns on record in 2021. Anglers and others grappling with wild steelhead conservation must keep in mind that a complex set of factors has caused, and continues to contribute to, these declining populations.

Wild steelhead are highly-adapted creatures living in a complex ecological network, so protecting and rebuilding decimated runs will require attendance to not just one, but all the pieces of the puzzle. Some pieces of the puzzle are more in our immediate control than others and every watershed faces different combinations of impacts.

And it should be obvious that all factors contributing to wild steelhead declines interact and compound with one another - so addressing, or not addressing, each piece ultimately impacts others.

So the challenge to recovering wild steelhead, and their home waters, is recognizing and acting with this awareness. We must act immediately on the factors we can control in the near term so the fish have the ability to respond in the longer term to continued improvements and investments in recovery, and to adapt and survive changes in the environment, especially the accelerating impacts of climate change in both freshwater and ocean ecosystems.

Pieces of the Puzzle

Directed Harvest

Exploitation from fishing, both legal and illegal (poaching), obviously reduces populations. Directed fishing effort not only impacts the numbers of returning adult spawners, but also the resident form of young steelhead in rivers and their tributaries. Where runs are intensively managed to provide fisheries, the application of Maximum Sustained Yield (MSY) has failed due to a focus on maximizing short-term opportunities, based on abundance. This practice ignores mixed-stock diversity which erodes long-term sustainability and on the misconception of “surplus” yield.

Catch-and-Release Impact

Many anglers who practice catch-and-release (CnR) fishing for wild steelhead may assume no impact. However, studies on steelhead survival put estimates of the direct lethal impact from CnR around 10% (findings range from 3.4% to 23.15%). CnR studies on resident rainbow trout suggest even higher lethal and sublethal effects. Further, stress levels—from long fights, difficult hook removals, and air exposure—increase stress hormone levels that can produce poorer egg conditions and sperm counts. These effects are compounded in many systems where throngs of well-intentioned fishermen can handle some individual steelhead multiple times, with compounding impacts on productivity.

Dams/Barriers

Either by complete physical blockage or acting as major impediments to migration, dams and other barriers have single-handedly decimated steelhead and salmon numbers and altered the evolution of wild steelhead traits such as fidelity to natal streams, adult spawn timing, embryonic development rate, and juvenile migration strategies. By disrupting the flow of water, large reservoirs and dams fundamentally alter temperature regimes and flow conditions. Dams and barriers also introduce artificial pinch points where migrating fish become easy targets to predators such as sea lions and seals, or structures like Washington’s Hood Canal bridge block out-migration of steelhead and salmon.

Land Use Impact

Human development in watersheds continues to erode river, tributary, and estuary habitats. Through extensive logging, urban development and agricultural modifications, river habitats are destroyed or otherwise degraded to the detriment of ecosystem function. Together, changes such as organic and other pollution, thermal loading, channel modification, removal or altered riparian vegetation, and altered hydrology combine to severely reduce steelhead productivity - a species that depends on the freshwater part of their life stage for spawning, nursery areas, and time as resident rainbow trout. Obviously, protection and restoration of in-stream habitats are critical investments for wild steelhead, and salmon populations.

Stream Temperature

Exposure to increasing river and stream temperatures, both in spikes and long-term averages, impacts steelhead spawning, rearing, and migration habitats. Increased river temperatures and low flows often work together - reducing preferred thermal habitat and severing necessary connections between habitat areas that otherwise were used to provide sanctuary. Hot water can devastate juveniles rearing in the river and harm the returning adults. Hot water temperatures can compound angling impacts, too, with documented higher mortality from angler encounters.

Snowpack Level

In many watersheds inhabited by steelhead, snowmelt produces more of the annual runoff than rainfall. Climate models now predict declining snowfall with about a 25% reduction by 2050, and low or no snow conditions becoming persistent in 35-60 years if greenhouse gas emissions continue unabated. Obviously, a shift in the precipitation phase from snow to rain leads to significant decreases in annual streamflow and altered hydrologic cycles - a trend that has clear implications for anadromous steelhead who depend on steady flows and safe temperatures for spawning and rearing as juveniles in freshwater.

Hatchery Genetic Impact

Studies have clearly shown the distorting effects of artificial propagation on steelhead genetics. We must now also consider epigenetic programming and inheritance effects from artificial propagation. Epigenetic effects are alterations in how an animal’s genes are expressed in response to its environment. For steelhead spawned and reared in the domesticated setting of a hatchery, these changes include shifts in age at spawning, body shape and physical characteristics, abnormal growth rate, brain development, lack of anti-predator behavior, and tendencies to stray, among others. Unfortunately, these distorted traits can be passed on, even to wild steelhead, which manifests in not just poor survival of offspring but in overall fitness.

Hatchery Fish Competition

Negative influences of hatchery steelhead on wild stocks have been shown to include increased competition and predation. Production hatchery practices to support the demands for a fishery fail to recognize the intricate food webs that are now being forced to accept artificial inputs of hatchery fish. Ecologists have long been concerned about hatchery fish impacts in freshwater, but increasingly, wild steelhead advocates should be concerned about the impacts on the ocean food web also from record numbers of pink and chum salmon being stocked in the ocean to support commercial fisheries.

Pinniped Predation

Harbor seal and sea lion populations have increased since the inception of the Marine Mammal Protection Act in 1972. Burgeoning populations of these protected marine mammals have been found to be a significant factor in declined steelhead survival, especially in the Salish Sea and the Columbia River. When pinnipeds feed on steelhead, they’re targeting not just vulnerable young steelhead, but they also are attracted to the runs of returning adult fish.

Ocean Conditions

The world’s oceans are at record temperatures. Increasing persistence and magnitude of marine heatwaves have real implications for altering the marine food web - mainly through overall lower ocean productivity and in observed shifts in the ranges of different species, including steelhead. Oscillations in surface currents - the large oceanic gyres - also have influence not only on productivity but also on heat transfer and the transport of productive plankton. Warmer water produces stagnant nearshore areas susceptible to anoxia and harmful algal blooms - as observed recently with the well-documented 'Blob' - with poorer conditions for out-migrating steelhead smolts. Offshore, projected climate changes are expected to reduce favorable thermal habitats by 36% during winter for steelhead in the North Pacific. Ocean oxygen levels are projected to decrease by as much as 3.5%. Unprecedented increasing latent heat in the ocean will continue to impact trade winds, ocean currents and transport, oxygen content, and overall productivity.

Ocean Acidification

The rate of acidification of seawater is unparalleled in at least the past 66 million years. Impacts from increasing ocean acidification, from increased atmospheric carbon dioxide, are going to affect the open ocean and coastal food webs. Organisms directly affected by declining ocean pH include invertebrates that play a significant role directly or indirectly in steelhead diets. Physiological effects of acidification may also directly impair steelhead olfaction (sense of smell), which could impact homing ability.

Estuary Habitat

The overall productivity of anadromous steelhead is based largely on growth attained in freshwater habitats during their early life history. Studies show that estuaries, in particular, afford a key, critical habitat for smolt growth in preparation for the transition to saltwater. Maintenance and restoration of estuaries provide important nursery habitats for producing larger smolts with subsequently increased ocean survival.

Encroaching Warm Water Species

With climate change, increases in water temperature is starting to expand the range or increase the population size of warm-water fishes and also increase their predation rates or competitive effects on species like steelhead that prefer cool water. This involves both the river and ocean environments. Tropical and subtropical marine fish are now being found off south-east Alaska, and, non-native predators, such as smallmouth bass, walleyes, striped bass, and catfish, and competitor fish species, such as American Shad are of concern in rivers like the Columbia. Impoundments produce thermal habitat changes more favorable to these introduced species and inadvertently provide more of an advantage for native species like the predatory northern Pikeminnow.

Lack of Salmon

The anadromous cousins to steelhead, Pacific salmon play an important beneficial ecological role in western watersheds. After generations of salmon population declines, (for many of the same reasons as steelhead) western watersheds are starved for the nutrients delivered by salmon. Recovering steelhead, and functioning ecosystems, requires that we also recover salmon. These species are intertwined. Fortunately, much of the work to protect and restore steelhead populations benefits salmon as well. Salmon also buffer predation by marine mammals, including southern resident killer whales. Chinook salmon are the primary species detected in resident killer whale diet samples, but studies indicate that the whale diet diversifies to include steelhead, when Chinook are less abundant.

The Completed Puzzle: A Return to a Fish in Full

Steelhead are challenged by an array of environmental changes and anthropogenic stressors. The mosaic of interwoven factors described here are all part of the puzzle that determines the fate of wild steelhead and their home waters.

Many of these impacts are chronic and cumulative (overharvest and dams, as example). Some, like ocean conditions, have received increasing attention in recent years and are adding to our understanding of the suite of stresses placed on wild steelhead populations. Unprecedented low numbers of returning fish leave us with very small margins of error and make every impact (and every successfully spawning wild fish) critical. The accelerating effects of climate change adds urgency to every one of the puzzle pieces.

Our job as dedicated anglers is to develop a full awareness and, where needed, support necessary conservation measures in the short term to give the fish room and necessary sanctuary to recover for the long term. We take great care when we are on the water, but off the water we must also take the responsibility to force managers, agencies, and political leaders to not only make the immediate management steps when escapement levels are not being met, but more importantly to also make the investments required to heal watersheds and to address the full suite of issues required to rebuild, recover, and encourage long-term robust runs of wild steelhead.

Wild steelhead are up to the challenge. Their diversity and time-tested evolutionary match to their home waters is the key to their survival. As advocates, understanding how all of the pieces of the puzzle fit together and, importantly, how they all interact, is important because it helps us avoid the trap of overly simplistic solutions and aimless finger pointing. When seen in all its parts, the puzzle illustrates the need for comprehensive restoration, transformational changes, and resource management focused on all facets necessary for recovering populations and protecting and healing watersheds above all else.