This writing documents various speculations about summer steelhead made at various times over the last dozen or so years. They are variably wild speculations so expect some loose ends. The purpose of this piece of writing is to propose some tenuous connections between the life habits of summer steelhead, their evolution and ecology; not to produce an even butter knife-sharp logical paper.
Seven Species of Pacific Salmon
On the eastern rim of the North Pacific Ocean there are seven species of Pacific salmon that return to their natal rivers and creeks. These are Oncorhynchus clarki, the cutthroat trout; Oncorhynchus mykiss, the steelhead/rainbow trout; Oncorhynchus tshawytscha, the chinook salmon; Oncorhynchus kisutch, the coho salmon; Oncorhynchus nerka, the sockeye salmon; Oncorhynchus keta, the chum salmon; Oncorhynchus gorbuscha, the pink salmon.
To simplify what will be a discussion of primarily the steelhead life form of the rainbow trout herein, and where I will be distinguishing between the steelhead/rainbow and the cutthroat trout on the one hand and the chinook, coho, sockeye, chum, and pink salmon on the other, the former will be referred to by the made-up term Pacific trout and the others as the other Pacific salmon. As a final terminological distinction, the term pristine will be used to describe native, naturally propagated fish and their gene pools which have never incorporated genes from an artificially propagated or reared fish. One hundred thirty-five years of hatcheries for Pacific salmon on the west coast of North America have changed pristine salmon from the only type of salmon in existence to what is for the most part a theoretical entity . The concept, pristine salmon, remains an important one since it references the point truly on the other end of any spectrum from the artificial, or domesticated, fish—now the rule in the North Pacific Ocean.
Pacific trout are generally differentiated from the other Pacific salmon by spawning around the time of the vernal equinox and by not necessarily dying after spawning—though, along the coasts of Oregon and Washington only about 15% of the steelhead survive and make it back to the ocean—by their relatively large life-history diversity with both resident and anadromous varieties of each species, and by their forming a relatively small portion of the anadromous Pacific salmon roaming the North Pacific Ocean in early historic times, say five hundred years ago. Thus with minor exceptions, the other Pacific salmon can be generally characterized by their spawning from late summer to early winter and by uniformly dying after spawning; with the possible exception of chinook, by having relatively limited life history diversity with primarily anadromous forms; and by making up the dramatically dominant portion of the Pacific salmon in the North Pacific Ocean in early historic times. Each of the other salmon species was far more numerous than the steelhead and chum, sockeye, and pink salmon are by much more abundant than the chinook and the coho.
The greater population numbers of the other Pacific salmon make it clear that spawning and uniformly dying has been a positive adaptation for these fish. One of the mechanisms for the success of this particular adaptation may be the fertilization of the natal reaches of the notably nutrient-poor streams of the Pacific Northwest with marine-derived nutrients found in the carcasses of the parental generations. In a sense this process of fertilizing natal stream reaches can be viewed as a kind of contrary parenting by the dead salmon. Please note that originally the pristine numbers of Pacific salmon that ascended the streams flowing into the North Pacific Ocean dwarfed present numbers and, again, they were all wild fish.
The Ancestral Form of Pacific Salmon
The Pacific trout are the living species closest in form to their common ancestor with Atlantic salmon and brown trout and, thus, they are a more ancient form of Pacific salmon than are the other Pacific salmon. Interestingly, the chinook and the coho appear to be accepted as the next most ancient Pacific salmon species and it is these two salmon that most resemble the rainbow in their juvenile life histories.
The fact that the Pacific trout can be considered similar to the ancestral form of the other Pacific salmon suggests that, before the proliferation of the many species in the Pacific salmon genus, the primal Pacific salmon may well have exhibited a broad range of life histories which exhibited both resident and anadromous forms, spawned in the spring, survived this spawning at some level, and, while they may have been an apex fish species in their freshwater habitats, they probably weren't present in their marine environments in anywhere near the numbers that Pacific salmon were five hundred years ago in the North Pacific.
It is almost as if, the life habits of each of the other Pacific salmon has specialized in a specific and a different portion of the broad range of life habits present in the Pacific trout species. Furthermore, as one examines the specialization in life habits that characterize the progression of Pacific salmon species from the oldest—the Pacific trout—through the chinook, to the coho, to the sockeye, to the chum, and ultimately to the pink salmon; it is quite clear that the juvenile life histories have evolved to make less and less use of the freshwater stream environment and, with the specialized exception of the sockeye and their lakes, earlier and earlier migration to the estuarine and marine environments.
The Advantages of Anadromy
Anadromy, a life habit where a fish is born in freshwater, moves to saltwater, and returns to freshwater to spawn, is common to fish of the salmon family. Generally, in the Pacific Northwest, the ability of a freshwater species to go to the ocean allows increased growth over what is possible in freshwater and this growth allows the storage of increased reserves of energy for variably long migratory journeys in freshwater, journeys that are made without eating. Their ocean-derived size means, for the most part, that returning adult salmon have outgrown the ability to obtain significant nutrition from the lower productivity of freshwater habitats . Proof of this will be found in the fact that resident freshwater trout that have lived to the old age of eight or nine years rarely exceed a pound or two in weight and twenty inches in length. Steelhead are able to put on four to six pounds in a single year spent feeding in the marine environment. A further proof, and a great and a simple one, is found in Big Bend Pool itself. Every year three to five or six hundred wild summer steelhead gather in the pool for many months, fish that average eight pounds and twenty-eight inches in length. What conceivable food source is available to them—a food source that, additionally, has to be unavailable to the eighteen or so cutthroat trout present in the pool?
Another advantage to the greater size made possible by feeding in the much greater productivity of the ocean environments is the ability to carry increased numbers of gametes. A yet further advantage to marine size is as a relatively large reservoir of marine-derived nutrients which are deposited with their post-spawning demise in the area containing their eggs and, ultimately, their young. This is a rich fertilization of the stream and the near-stream terrestrial habitats that allows juvenile salmon increased opportunities for feeding and, in turn, lessens the amount of competition.
It is worth noting once more that the streams of the Pacific Northwest are the least productive in North America. Relative to other parts of the continent, streams on the eastern shore of the North Pacific Ocean are high gradient, cold and rapid, nutritionally poor, and depauperate in fish fauna. Part of the reason for this is that the Pacific Northwest is also the most tectonically active portion of North America. Additionally, the dominant fish faunas of Pacific Northwest streams are genera that exhibit either anadromy or a tolerance for brackish water, and show an ability to colonize new freshwater habitats. Taken together, to me, these things suggest strongly that, besides allowing for greater growth and accumulation of reserves of energy, the marine environment presents a seasonal and annual stability not found in freshwater habitats.
Perhaps the ocean is even a refuge for those fish species capable of making use of it. A very strong bit of evidence for this is that the Pacific salmon fresh and weak and less resilient from the hatcheries surrounding the North Pacific Ocean—seemingly—do well in it . . . if the marine productivity is good and the upwelling events happen. In a terrible travesty of the pristine numbers of Pacific salmon—at least ten to twenty times the present numbers of returning adult Pacific salmon—approximately, five billion hatchery smolts are flushed into the marine environments around the North Pacific Ocean every year. Another piece of evidence that the North Pacific Ocean is perhaps a rest cure for Pacific salmon is the fact that around 95% of the mortality of any wild population of Pacific salmon occurs in freshwater prior to smolting up and entering the salt.
Now I am going to interject that hatchery managers and other game department people who make their money off running hatcheries and convincing the public that hatcheries are saving their fishing, have made and make a great big propagating deal about this 95% mortality of wild salmon before smolting. To it they compare the 95%+ of their hatchery spawned and coddled salmon that survive to the smolting stage . . . if everything in their complex engineered artificial-fish-production facilities works and the young domesticated salmon survive their first one or two years living in what to all intents and purposes is a disease vector-rich environment that requires constant flushing with antiseptics and the regular administration of antibiotics.
Wild, naturally propagated Pacific salmon fertilize the same percentage of their eggs naturally that artificial propagation does in its hatchery buckets. Wild natural propagation is free.
It is at this point—egg fertilization—that natural selective pressures begin to work and by the time smolting comes to a generation of wild salmon, the 5% or so that have survived the adaptive crucible of life in a freshwater stream are as strong and resilient as it can be. On a year of good ocean productivity—in reality—only 5% or less of the hatchery-spawned-and-reared domesticated salmon smolts return from the ocean as adults to entice anglers to the rivers of the Pacific Northwest with the promise of killing a fish. And the game departments want you to kill them, they say so, so domesticated fish don’t mix with the wild fish.
An Elegant Synergy
It is a quite elegant synergy within which large Pacific salmon richly fertilize the basins of their home rivers and each of the other Pacific salmon spawn in and fertilize different portions of these basins somewhat differently.
After the Pacific trout, the chinook salmon exhibits the greatest diversity of life-history types, though—with the possible exception of spring chinook—chinook do not generally get far into the headwater portions of their natal streams. These largest of Pacific salmon will travel hundreds of miles through mainstem reaches of rivers to return their eggs and milt and their carcasses to their natal reaches. Juvenile chinook exhibit a wide range of freshwater residence, from young-of-the-year that travel directly to saltwater after their emergence from the gravels, to young fish that spend a few months to a few years in freshwater before smolting and entering the ocean.
Coho have relatively simple life histories. Like the chinook, the coho salmon travels potentially well up into their natal stream basin, however, these fluvial systems are mostly coastal. When spawning in the same stream reaches, coho have a tendency to spawn at higher elevations than do the chinook. Juvenile coho spend at least their first year in freshwater.
Sockeye spend potentially as much time as juveniles in freshwater as do the most drawn-out residences of the chinook, but—here on the eastern edge of the North Pacific Ocean—their juveniles are specialized in lake-rearing. Chum are the most closely related to the pink salmon, but are potentially relatively long-distance travelers to their spawning habitats. On emergence from the gravels, most chum salmon fry travel directly to the ocean. Pink salmon have the least reliance on freshwater of all Pacific salmon. These salmon migrate relatively short distances into freshwater and their fry return to saltwater immediately on emergence. In contrast to all other Pacific salmon which emerge from the gravels with dark parr marks on their sides, parr marks and spotting that effectively camouflage them in freshwater environments, pink salmon emerge from the gravel with the silver sides, blue-green backs, and white bellies that other salmon achieve only on smolting prior to entering saltwater. Pink salmon are the smallest of the other Pacific salmon and they are the most numerous Pacific salmon found in the North Pacific Ocean.
As stated above, all the other Pacific salmon die after spawning and fertilize their particular stream reaches. Steelhead, being rainbow trout, do not die necessarily after spawning, but the weeks to months that adult steelhead hold in freshwater living off reserves without effectively feeding is an ordeal and, as a general rule, most individual steelhead of the various spawning runs here on the east side of the North Pacific will die. This post-spawning death is largely due to running out of energy before they can get back to the ocean, the only environment that has enough food to sustain and increase the reserves of these large fish that have outgrown the amount of nourishment offered by fluvial habitats.
Returning now to anadromy and the portions of their life histories that are spent in the marine environment, there is another way that the large size serves ensuing generations of Pacific salmon, a contrary way. Off the coast of the Pacific Northwest, when an individual salmon gets larger than around twenty-inches in length, it has largely outgrown its ability to feed effectively in freshwater. If this is true for an individual fish, how much more so is this true for the numerous fish of given spawning migrations. Again, what conceivable source of food is there in Big Bend Pool for the hundreds of wild summer steelhead that gather here for months.
The only common food source that might keep an individual adult anadromous salmon alive—if they needed to eat—is the resident fish in a stream and, in the time of the pristine runs, the dominant fish in any stream that supported runs of anadromous salmon would be the juveniles of those same salmon. So, the strong tendency of in-migrating anadromous Pacific salmon to fast in freshwater is in an explicit complementary relationship with the fertilization of the natal stream reaches with parental carcasses: anadromous adult salmon do not take anything substantive other than oxygen and space from fluvial habitats during their weeks or months in freshwater.
Now, having very generally reviewed the life habits of all the Oncorhynchus genus common to the eastern edge of the North Pacific Ocean, and noting again that present runs are made up mostly of hatchery fish and that the run sizes of the various Pacific salmon presently returning from the ocean averages around 3% to 5% of size of the pristine runs—yes, the hatchery managers of the various game departments have been pulling the wool over our eyes for human generations (admittedly, often through simply just not examining the most rigorous and most recent data)—think of what the recurring seasonal return of anadromous adults in their pristine numbers meant to the fluvial ecosystems and the near-bank terrestrial habitats of the streams they returned to. Consider just the energy derived from the stray eggs rolling out of the nests prepared for them and this nutritive influence on salmon fry and parr and the other native fish genera and species.
Wild-Onager Speculation #1.
Consider the potential influence of these pristine numbers of stray eggs on wild summer steelhead adults. Most of the summer steelhead leave the ocean in May and June and, as stated, do not feed other than incidentally in freshwater through the eight to nine months they spend waiting for their spawning time during the following spring. Now, it is abundantly clear that summer steelhead do not need to feed to make it through to their spawning time and to successfully spawn. When it is considered that the other Pacific salmon populations commonly begin spawning generally toward the middle of the sojourn of summer steelhead, it is quite possible that feeding on eggs might well give a summer steelhead a greater opportunity to survive to spawn again. Consider that repeat spawning would be an extremely effective way of ensuring the continuance of a summer steelhead population and the more repeat spawners the better. Stray eggs are the one food source that is present in the stream environment that does not directly come from the fluvial habitats and stray eggs do not ultimately cripple the breeding potential of a population of Pacific salmon since these eggs have already drifted from the shelter of their redds.
Wild-Onager Speculation #2.
Now for the background of my principle wild-onager speculation. Most anadromous Pacific salmon species rely on ocean productivity for the success of the marine portions of their lives and this productivity relies on ocean conditions which appear to be principally driven by coastal upwelling events off the coasts of Washington , Oregon, and California between the Straits of Juan de Fuca on the north and Point Arguello and the Santa Barbara Channel on the south. Off the coast of Oregon and Washington these upwellings are seasonal and pretty much confined to the late spring and summer. It has been accepted for the last twenty or so years in the scientific literature—a falsifiable literature that presents its data as opposed to the assertions that pass for rigorous study in game department newsletters and handouts—that seasonal upwelling events strongly enhance the survival of especially first-year Pacific salmon migrants. Furthermore, higher than average ocean surface temperatures—El Nino—seem to be correlated with the failure of these upwelling events.
Upwelling events are a response to the southward coastal winds of spring and summer which are generated by the North Pacific High Pressure Cell. Coriolis force—an inertial force produced by the spinning planet—acting on these southerly winds, deflects the upper twenty meters of surface water to the right in the northern hemisphere and off shore along the eastern shores of the North Pacific Ocean. This offshore movement of surface water causes the water from one to two-hundred meters deep to well to the surface, replacing it. This cooler nutrient-rich water fertilizes the phytoplankton which form the basis of the ocean food pyramid, setting off a period of extreme marine productivity.
Generally, the warm sunny days that characterize late spring and summer are associated with high pressure and functioning upwelling events. Contrarywise, overcast, with or without precipitation, from counter-clockwise rotating low pressure systems are associated with the failure of coastal upwelling. This clearly suggests that as upwelling-generated ocean productivity is interrupted, conditions in freshwater environments improve for stream-dwelling juvenile stages of anadromous Pacific salmon as well as for those adult summer steelhead and spring chinook that are maturing their eggs during their long-term residence in freshwater.
Now, the best description I have come across of the difference between summer and winter steelhead is that winter steelhead mature their gametes in saltwater while they are feeding and summer steelhead mature their gametes in freshwater while they are not feeding. A year or two ago, it jumped out at me while reflecting on this simple differentiation that the life habits of summer steelhead have them leaving the ocean in May and June, that is, summer steelhead are leaving the ocean prior to the balance of a given season’s upwelling events...if it is a season of average to good events. Could this early migration be an adaptation to those times when a season’s upwelling events are poor?
Summer steelhead timing for the ascent of their natal rivers would make the failure of a season’s upwelling of little consequence to them . Even if this early run timing is an adaptation by summer steelhead to the potential failure of coastal upwelling events, it is not the full story. Steelhead are known to spend much of the marine stage of their lives as pelagic creatures living off shore beyond the zone of upwelling. Nevertheless, it is worth remembering that the coastal distribution of steelhead populations is principally along the eastern edge of the North Pacific Ocean where Coriolis force makes coastal upwelling of various kinds possible.
Wild-Onager Speculation #3.
There are other potential adaptations to consider as well for wild summer steelhead populations. Another environmental situation to consider is the glacial history of the last six million years of the Plio-Pleistocene. Very roughly, this time has experienced the regular repetition of glacial cycles, each lasting tens of thousands of years. During these glacial events, when continental and alpine ice sheets were advancing or retreating—true for the balance of this time—the high flows in affected fluvial systems would have been in the summer with most of the precipitation stored as snow and ice in the winter. During the most recent glacial maximum, it was primarily the land masses on the middle and the northern portion of the eastern edge of the North Pacific Ocean—now known as Alaska and Canada—that were buried by continental ice sheets with the Cascade and Sierra Nevada mountain ranges locked in alpine ice sheets above 5,000 feet above mean sea level. The Asian land mass off the western edge of the North Pacific Ocean remained largely ice free. As noted above, steelhead populations are most common presently throughout this previously glaciated area.
These high summer flows seemingly would favor the run timing of summer steelhead as that best suited to negotiating their way further up into their natal fluvial systems . . . if these natal systems were not completely covered by ice as were many of the streams of Alaska and Canada.
It is quite intriguing that, when the spawning habits of the various species of the other Pacific salmon are considered, the gradual encompassment of a given fluvial basin by a glacial episode would generally recapitulate the phylogeny of these salmon. As a glacial climate took hold and glaciers formed, the first populations substantially affected in a given fluvial system would be the chinook and the coho salmon, while the last to be affected would be those Pacific salmon with the least need of fluvial habitats for the rearing of their offspring—the most recently evolved chum and pink salmon.
This piece of writing has allowed me to propose some connections between Pacific salmon evolution and various natural history data and physical processes, propose them in the form of speculations. While these speculations cannot be the whole picture, and may not be any part of it, I have tried my best to present the foundations on which they are built.
Take care and go well,
August 22, 2010
Augerot, Xanthippe, Charles Steinback, and Andrew Fuller
2005 Atlas of Pacific salmon. University of California Press, Berkeley
1999 Salmon without Rivers. Island Press.
National Research Council
1996 Upstream: Salmon and Society in the Pacific Northwest. National Academy Press, Washington, D.C.
2005 The Behavior and Ecology of Pacific salmon and Trout. American Fisheries Society in association with the University of Washington Press, Seattle.
1991 Pacific Salmon and Environmental Change in the Rogue Basin, Lee Spencer Archeology Paper No. 1991. Prepared for the Southern Oregon Historical Society.
Excluded from consideration in these speculations are the relatively small numbers of residualized anadromous Pacific salmon and those Pacific salmon that spend only a few months in the estuarine or near-shore marine environments. These excluded life history types are often evolutionary failsafe mechanisms and play more complex games with adult size and feeding in freshwater.
The “half-pounder” steelhead of the Rogue, Klamath, Mad, and Eel Rivers are not adult fish, they are not on a spawning run, rather they are spending the time from late summer through the following spring feeding in their natal streams.
It is worth noting that the earlier migration of summer steelhead from the ocean pastures would also (and in a quite minor way) potentially make more nourishment available to—and reduce competition with—winter steelhead populations . . . if both varieties of steelhead use the same portions of the North Pacific at the same time.