Steelhead’s Missing Years
We steelhead anglers naturally focus on those magnificent bright chrome and crimson summer and winter run adult steelhead just emerging from their time at sea. The source of our passion regarding issues that determine steelhead fate is focused on this particular part of their life history. Such devotion is understandable, given the charismatic nature of this beloved, powerful sea run fish and the gratifying moment of connecting with one streamside after all those casts. This obsession on spawning-run steelhead is reinforced by savvy marketing by guides, lodges, and equipment dealers, not to mention all those management conventions such as “escapement” and “redd counts” or even the feeder-lot designation of “brood stock.” We at the Wild Steelhead Coalition also employed spectacular images to advance the cause of conservation.
But this narrow focus may overlook a fuller understanding of the complex life history of steelhead. Or suppose an angler does pay attention to such. In that case, it usually extends to concerns of their time at sea, as the changing ocean conditions have become highlighted in both scientific as well as popular media. This increased awareness is still only the proverbial tip of the iceberg.
When is a Steelhead Not a Steelhead?
Most anglers reading these pages likely have an understanding that the species Oncorhynchus mykiss exhibits a complex of reproductive behaviors that generally involve summer-run steelhead, winter-run steelhead, and resident rainbow trout that incredibly all can spawn in the same river. Fine, but is it a case that ‘never the twain shall meet’? And if not, what differentiates young steelhead from resident rainbow trout in such river systems?
It's complicated. A standard rule of thumb is size. Sizes of steelhead smolts do run around 8 inches. But it is not necessarily simply size, obviously, as this overlaps with young resident rainbow trout. Research has also found conclusive evidence that, in some populations, non-anadromous resident females (rainbow trout) produce steelhead progeny, and conversely, steelhead females produce non-anadromous progeny. And sex: there is strong theoretical and empirical evidence that females are more apt to benefit from anadromy, despite the greater risks in the ocean environment. Besides genetics, there seems to be primarily a metabolic stimulus at work here - more freshwater food, less stimulus to migrate. Skinny fish run to the sea (steelhead); fat fish stay (resident trout).
So, how long are these fish resident in freshwater before smolting? Across their native range, freshwater residency for steelhead can span anywhere from one up to 4 or more years (as revealed from tagging studies and scale growth pattern analysis). The result is that each spawning year produces successive year classes that contribute to the population of resident trout - adding individuals to those previous year classes still residing in their natal streams. This reproductive strategy builds up a multi-cohort bank of young steelhead and trout in each watershed. Literally reproductive money in the bank.
Further, this strategy results in resident steelhead populations that are ecologically tuned to the various conditions within each watershed. A good example is a study of wild fish in the Skagit River where smolt trapping locations further upstream or at higher elevation (Bacon and Illabot Creeks) had, on average, earlier catch dates than a lower tributary (Finney Creek). Matching this trend was the mainstem trap, where steelhead catch had the latest catch date. Also, the higher elevation and colder water tributaries of Illabot and Bacon creeks had more age-4- and age-3 smolts than Finney Creek and the mainstem trap. Steelhead smolt population age structure was different in each sampled tributary.
However, the role of residency can be influenced by other conditions. There is evidence from California (Eel River) that dams, and their impoundments, shift the environment to one more conducive to residency. Also, some steelhead stocks in British Columbia have been shown to shift away from anadromy at low population abundance (i.e., remaining freshwater residents). It is indeed complicated!
The significance on the overall stock status of these observations should be obvious, and the impact from recreational trout fishing becomes evident. As resident fish, they are exposed to numerous incumbent stresses in this overlooked segment of their life history. One obvious conservation measure we have immediate control over is fishing mortality. In one study in Idaho, hooking mortality rates were 4-6 % for flies and lures, respectively, to around 25% for bait-caught resident trout. The implications here are clear.
Do the Math!
The number of steelhead that survive and return to spawn relative to the number of juveniles that migrated to the ocean is known as the smolt-to-adult ratio or SAR. In some systems, the numbers of smolts are counted directly, but in many, it is calculated as the numbers of returning adults of the same cohort from a given brood year. Broadly, SAR is reported to range anywhere from 1 to 10% in wild populations. It is widely held that a SAR of 4 to 6 percent (that is, for every 100 smolts, 4 to 6 adults return to spawn) is a highly desired objective for robust populations, where a SAR of 2 percent is needed just for replacement – the biological equivalent of treading water. Less than 2 percent, and the ship is sinking.
In understanding these ratios, it becomes evident that reductions in numbers of young resident rainbow trout can and does have a proportionally large impact on the number of returning steelhead adults, particularly at lower levels of SAR. And this necessarily also involves any non-anadromous resident O. mykiss, as remember, it is documented that these fish are an essential contributor to progeny that eventually become anadromous! Speaking of math, such complexity in steelhead life history also has profound implications for the stock-recruitment models currently used to establish escapement and harvest levels. This life-history complexity, including repeat spawning, exhibited by steelhead may not lend well to the use of traditional spawner-recruit models, even with more sophisticated approaches now in use.
Read and Heed
It really is an egregious oversight to advocate for the protection of spawners as means to get sufficient numbers of these fish on gravel, then abandon any concern for their resulting resident progeny - progeny that spend several years in their natal streams and tributaries. We steelhead anglers are fixated on the spawning runs. It’s time we start to become similarly fixated on those resident fish. But this really is nothing new. The necessity of a strategy that integrates the management of non-anadromous and steelhead rainbow trout was recognized by John O. Snyder (California Fish and Game), who made this insightful yet mostly unheeded statement in 1928:
"We have steelheads and stream trout, and conservation of the one depends absolutely upon the conservation of the other. We burn the candle at both ends when we overfish both the steelheads and stream trout. We are awakening to the fact that we cannot both destroy the steelheads and maintain the rainbows."
It is time we heed these wise words. It needs to be again recognized by all steelhead anglers that this life-history phenomenon is a clear strategy that results in population diversity designed to dampen fluctuations in abundance in what scientists call “portfolio effects.” Conserving resident trout, particularly in watersheds with wild steelhead runs, produces genetic integrity that, coupled with preserved or recovered river habitats, will go a long way to ensure viable steelhead populations, particularly in the face of inevitable environmental variability.
We cannot claim “Mission Accomplished”solely by getting fish on gravel. At this point, our job has just started with the need to conserve resident rainbow trout and recognize their contribution to the complex life history of wild steelhead. They are, after all, one in the same.
Further Reading