Rainbow Trout: What, Exactly, Are We Protecting?

On a recent weekend trip through the Pacific Northwest I stopped at a magical place in Portland known as Powell’s City of Books. With four floors of reading material, I couldn’t help but saunter a bit, even taking a moment to browse the rare books collection that included, among other marvels, an edition of Pliny the Elder’s Historia Naturale circa the 1600s.

In the end, though, I was choosing between three books: a survey of global stream ecology, an American Fisheries Society survey of watershed restoration practice, and a narrative work by Anders Halverson, entitled An Entirely Synthetic Fish: How Rainbow Trout Beguiled America and Overran the World. Pragmatism aside, I chose Halverson’s work (perhaps I was just seeking relief from my complete immersion in scientific literature of late). It has proved to be not only an entertaining read and valuable history lesson but also a tremendous thought exercise in relation to my own work.

Livingston Stone established a hatchery on the Upper McCloud River (in the Sacramento River Basin) in the late 19th century. Initially established to restore Atlantic salmon stocks with Pacific salmon species, his hatcheries would become some of the first from which rainbow trout would become stocked on a widespread basis. (Photo: CDFW)

Livingston Stone established a hatchery on the Upper McCloud River (in the Sacramento River Basin) in the late 19th century. Initially established to restore Atlantic salmon stocks with Pacific salmon species, his hatcheries would become some of the first from which rainbow trout would become stocked on a widespread basis. (Photo: CDFW)

Patty Limerick, the Faculty Director and Chair of the Board of the Center of the American West at the University of Colorado Boulder, accurately frames Halverson’s narrative surrounding the rainbow trout’s world takeover as a valuable precautionary tale. Natural resource management, particularly in the American West, has had no shortage of trial and error. Take the disastrous results of the early efforts of influential conservationists to control predator populations throughout the West, for example.

The decisions of well-meaning resource managers to eradicate predators resulted in immense numbers of starving and diseased elk, deer and antelope across the West. Because their numbers were no longer controlled by predators like bears, wolves, and lions, the game animal populations exploded and then subsequently collapsed to even fewer numbers than ever. Predators played an integral part in maintaining overall herd health, something of a revelation at the time.

This marked the beginning of a new era of understanding in ecology, one that would begin to acknowledge the great complexity of natural systems. Halverson’s book contains numerous lessons about both the complexity inherent to natural systems as well as the cascade of error in management that has (and still can) arise when this complexity goes unacknowledged.

M. Cerebralis, the agent parasite for the often fatal whirling disease, is thought to have come to the U.S. from European hatcheries in the 1950s. Once here, it quickly became a problem for hatchery operators and, due to wanton stocking efforts, a threat to wild trout populations. While there are a few locations in the Upper Feather River Basin where M. cerebralis is known to be found, UFRBWA aims to establish understanding of Basin-wide distribution of the pathogen through it’s eDNA sampling effort. (Photo: Wikipedia)

M. Cerebralis, the agent parasite for the often fatal whirling disease, is thought to have come to the U.S. from European hatcheries in the 1950s. Once here, it quickly became a problem for hatchery operators and, due to wanton stocking efforts, a threat to wild trout populations. While there are a few locations in the Upper Feather River Basin where M. cerebralis is known to be found, UFRBWA aims to establish understanding of Basin-wide distribution of the pathogen through it’s eDNA sampling effort. (Photo: Wikipedia)

Tracing from the fish culturing practices in 18th century Europe, he elucidates how fish propagation later became a matter of national importance for the newly-formed United States of America. He moves on to describe efforts to rebuild decimated Atlantic Coast fisheries with Pacific salmon stock from our own neighboring Upper Sacramento River. Happenstance amid those efforts found the rainbow trout to be a hardy, aggressive, easily-domesticated alternative when efforts to stock other Pacific salmon failed.

Halverson explains how social convention elevated the rainbow trout to the realm of premier game fish, the pursuit of which defined a gentleman, and how, in the end, the longevity of such conventions prompted resource managers to enact sometimes disastrous management decisions in favor of rainbow trout over other native biodiversity across the West.

The most potent lessons found in the history of artificial propagation of rainbow trout can be found within the wholly unintended, and for a long-time unnoticed, consequences of proliferating the species. Halverson outlines the story of three of these devastating wake-up calls for fisheries managers.

The first, involves the spread of Myxobolus cerebralis, the agent parasite that causes (the most-often fatal) whirling disease, first through hatchery systems all across the world and subsequently into the wild due to wanton stocking practices. The second is the significant loss of biodiversity among the other native salmonids of the West due to hybridization with rainbow trout, not to mention, the dilution of genetic stock among wild populations of rainbows themselves. The third is the un-monitored impacts of rainbow trout stocking on taxa other than fish, most notably the endemic amphibian species of California and the rest of the West.

Extensive stocking of rainbow trout has led to the proliferation of hybrids like this ‘cutbow,’ a common occurrence in the native range of the cutthroat. Hybridization of hatchery stock with wild rainbow trout poses the risk of diluting the genetic diversity of rainbows across the species’ own native range. As part of UFRBWA I have been attempting to establish the relative magnitude of stocking efforts across the Basin, in an effort to determine where observed wild populations of rainbow trout may have incurred little or no hybridization. (Photo: Wikipedia)

Extensive stocking of rainbow trout has led to the proliferation of hybrids like this ‘cutbow,’ a common occurrence in the native range of the cutthroat. Hybridization of hatchery stock with wild rainbow trout poses the risk of diluting the genetic diversity of rainbows across the species’ own native range. As part of UFRBWA I have been attempting to establish the relative magnitude of stocking efforts across the Basin, in an effort to determine where observed wild populations of rainbow trout may have incurred little or no hybridization. (Photo: Wikipedia)

Most of this grand history lesson applies directly to the fisheries of the Feather River Basin. Extensive stocking has established non-native trout and other fishes in the Basin, efforts that concomitantly also introduced M. cerebralis. The stocking of rainbow trout has also certainly resulted in hybridization with true native populations, the extent of which is not known (although a recent study sheds a favorable light). Eradication efforts have taken place in the Basin to eradicate fish in the preservation of native amphibians.

So, amidst this history of inadvertent (and, yes, sometimes advertent) blunder of uninformed fisheries management, particularly surrounding rainbow trout (the eradication of which is a huge concern in water bodies where they are not native across the globe), the question arises: “What are we protecting?”

Well, at its core, the Upper Feather River Basin-Wide Native Fish Assessment and Improvement Strategy is meant to be, in small part, counteraction against this history of uniformed fisheries management strategy. The result, hopefully, will be the right knowledge and information to know where we can achieve the most bang-for-the-buck in protecting and improving wild rainbow trout populations here in their native range.

Mountain yellow-legged frogs are native to the Sierra Nevada. In the mid-90s Roland Knapp, a researcher working with the University of California and California Department of Fish and Wildlife discovered that the extensive fish stocking of high mountain lakes in the Sierra Nevada had likely decimated the species. Extensive efforts to reverse that trend are now underway. The results of the UFRBWA may be used in comparison with the results of similar efforts surrounding other taxa to ensure that fisheries restoration does not result in the decline of other species of concern. (Photo: Wikipedia)

Mountain yellow-legged frogs are native to the Sierra Nevada. In the mid-90s Roland Knapp, a researcher working with the University of California and California Department of Fish and Wildlife discovered that the extensive fish stocking of high mountain lakes in the Sierra Nevada had likely decimated the species. Extensive efforts to reverse that trend are now underway. The results of the UFRBWA may be used in comparison with the results of similar efforts surrounding other taxa to ensure that fisheries restoration does not result in the decline of other species of concern. (Photo: Wikipedia)

To the greatest extent possible we’re hoping to account for the intended and unintended consequences of historical decisions in fisheries management to ensure we’re doing so effectively. We think that this can be accomplished by identifying the distribution of pathogens, probable populations with low or no hybridization, as well as accounting for the impacts on other native taxa, before expenditure on any restoration can take place.

Often when I speak to people about my work, a similar set of questions arises. The first questions relate to the decline in stocking efforts by resource managers. People also often allude to the contentious management practice of poisoning water bodies (often done in the past to ensure the success of new stocking efforts). They often point out the folly of emphasizing continued preservation in systems that are, arguably, so altered that it is illogical to do so.

It’s true, in reality there exists a history of resource management that will be impossible to escape. Many of the decisions being made by fisheries managers these days are all part of effort to proceed with caution until the trajectory of this history is better understood.

One of the graces of Halverson’s work is that it distills the complexity of a particular history, that surrounding the propagation of rainbow trout, into a compelling narrative. It offers a resource for people like myself to share with others in an effort to provide contrast with business-as-usual management practices based on social convention rather than an understanding of ecology. In many ways, it sheds a real light on the value and necessity of efforts like the Upper Feather River Basin-Wide Native Fish Assessment and Improvement Strategy.

Better than that, it’s not a scientific journal article.