Guest Species – What about the nonnative species we like?

by Karrigan Bork, JD, PhD

Striped bass – One of California’s guest species.

Conservationists worry about a host of nonnative species, and with good reason. Nonnative species cause north of $120 billion per year in damages in North America alone, and they present the primary extinction risk for roughly half of the threatened or endangered species in the United States.

The worst offenders are well known – aquatic species like zebra mussels and Asian carp, and terrestrial species like kudzu, yellow star thistle, and myriad rat species. But there’s another category of nonnative species, species that we celebrate and enjoy.

“Guest species” describes naturalized nonnative species that humans have introduced, intentionally or accidentally, and which we actively conserve because we benefit from having them in the wild. This isn’t just semantics; the terms we use to describe a species play a central role in determining how we think about that species.

Pheasants are another guest species in the United States that have acquired iconic status.

Guest species include intercontinental introductions like honey bees, earth worms, pheasant, wild horses, and brown trout; and many other species that we’ve moved around (directly or via habitat modification) within North America, like striped bass, largemouth bass, turkey, and deer. These species are well-loved, culturally significant, and may play important roles in their new ecosystems.

But they also create significant conflicts for aquatic ecosystem management, and these conflicts often crop up as part of our most heated debates about how we manage our natural resources. My recent paper on guest species undertook case studies of several of these conflicts, including management of striped bass in California’s Delta and rainbow trout in Utah’s Green River. These two case studies highlighted several common themes in dealing with guest species that help to explain why they breed so much conflict. Top themes include:

  1. federal oversight of state wildlife management breeds conflict;
  2. people love their guest species, which increases conflicts;
  3. guest species can eventually become part of the local ecosystem; and
  4. guest species may be better adapted for the current environment than native species.

Guest species are particularly prevalent among aquatic species, which makes this a central issue for watershed scientists. Introduced fish species make up anywhere from 10% of the total species in eastern areas up to 30–60% of fish species in the west, and most of these transplanted species were introduced as game species or forage for game species.

UC Davis fish ecologist Carson Jeffres with a Delta striped bass. Photo by Martin Koening

Striped bass came to California via railroad in 1870, brought by Livingston Stone at the suggestion of the California State Board of Fish Commissioners. Striped bass populations exploded, and the population supported a commercial fishery for many years. Striped bass remain among the most popular California game fish, and 81% of fisherman near striped bass fish for them, with an average expenditure of $146.91 per day.

In 2008, the Coalition for a Sustainable Delta filed suit against the California Department of Fish and Wildlife, arguing that the state’s fishing regulations for striped bass amounted to a violation of the federal Endangered Species Act (ESA). The Coalition, a group of agricultural water users, seeks to “to better the conditions of those engaged in agricultural pursuits in the San Joaquin Valley by ensuring a sustainable and reliable water supply.”

The Coalition argued that the lawsuit was a way to improve the numbers of listed species in the Delta, which would in turn allow the coalition members to divert more water from the Delta. However, the lawsuit looks more like an effort to separate striped bass fishermen from the rest of the sportfishing community, which would reduce the community’s strong opposition to many Coalition positions. Regardless, the lawsuit was a bombshell for wildlife managers in California and across the country.

The Coalition’s theory of the case goes like this: the ESA bars any killing of any endangered species of fish or wildlife without a permit; the state catch and size limits increased the number of striped bass in the Delta; increased numbers of striped bass eat increased numbers of threatened and endangered species; therefore, the state regulations protecting striped bass amounted to state actions that kill endangered species in violation of the ESA. This line of reasoning was successful in a similar case in Hawaii.

But if courts generally accept this line of reasoning, virtually any management of game species could amount to a violation of the ESA, which carries serious monetary penalties and potential jail time. This could include management of native species as well – the law does not distinguish between native and nonnative species in this kind of conflict.

The Coalition’s lawsuit over striped bass ultimately failed. After the judge in the case signaled that the science on striped bass was too convoluted for easy resolution without trial, the parties settled the lawsuit in February 2011. Per the settlement agreement, CDFW recommended that the California Fish and Game Commission (an independent body which writes the sport fishing regulations in California) “modify the striped bass sport fishing regulation to reduce striped bass predation on the listed species.” See Coal. for a Sustainable Delta v. McCamman, No. 1:08-CV-00397 OWW GSA, 2011 WL 1332196, at *5 (E.D. Cal. Apr. 6, 2011). The Commission unanimously rejected the proposed change in February 2012, and although the court dismissed the case, the broader dispute remains unresolved.

This dispute highlights several of the aforementioned themes:

First, federal oversight of state wildlife management breeds conflict. Under the traditional North American model of wildlife management, state agencies, funded by hunting and angling licenses and special taxes, manage wildlife at the state level. This inherently creates some preference for game species at the state level.

When the federal government intrudes in the game management space, most often through the ESA, longstanding tensions between the state and federal governments can make the disputes worse. With striped bass, California once had an ESA permit allowing them to enhance striped bass populations via stocking, but abandoned that effort. Anglers at the state level, who had funded that effort with a special striped bass fee, blamed federal regulators for intruding on their fishery. This conflict is unlikely to go away and could easily spread to encompass other guest species. The Fish and Wildlife Service and the National Marine Fisheries Service should act now to clarify how the ESA applies to state management of game species and should, if necessary, work with state agencies to permit (and mitigate for) these activities.

Second, people love their guest species, which increases conflicts. As with the striped bass, many aquatic guest species were introduced into new ecosystems as game species for our fishing pleasure, and this effort has been a success. Introduced game fish are well loved, with strong interest groups lobbying at the state and federal level on their behalf. The striped bass fan club in California includes the Sportfishing Conservancy, the California Sportfishing League, the Coastside Fishing Club, the California Striped Bass Association, and the California Sportfishing Protection Alliance, all of which lobby on the fish’s behalf.

Wild horses: another guest species of the American West with iconic status. Image source: Wyoming Public Media

This isn’t limited to aquatic species – Wyoming put the wild horse, a guest species, on its state quarter.

Because people love these guest species, efforts to reduce their populations or eliminate them entirely often run into stiff opposition, ranging from lawsuits to direct action, i.e. sabotage of removal efforts or reintroduction of the species. The flip side is that this same love of guest species brings people closer to their environments and can result in increased environmental activism, as seen by the sportfishing groups’ broader involvement in protecting the Delta ecosystem from pollution and water withdrawals. Guest species are a, and perhaps the, motivating factor for many casual conservationists today. Without these species, conservationists lose much of their public support.

Third, guest species can eventually become part of the local ecosystem. This is true in two ways – both in terms of the bass’s role in the ecosystem, and in broader philosophical terms. Scientists have a very difficult time predicting what would happen in the Delta ecosystem if striped bass were functionally removed. Although striped bass eat some listed species, they also eat predators on listed species, and so ecologists can’t accurately predict how striped bass removal would affect the populations of listed species. Ecosystems like the Delta “are so highly altered that attempting to restore them to an earlier condition or stable state is largely not possible.”

More broadly, striped bass have been in California for almost 150 years. Based on research on transplanted salmon populations, the California striped bass are likely adapted to the West Coast ecosystems and are likely genetically differentiated from their East Coast kin. These fish have adapted to their new habitats, and they have thrived in the current Delta, which offers habitat far different than historic conditions. The Delta today is a novel ecosystem, an ecosystem which lacks a historic analog.

If we think about native species as species that evolved in a given habitat, then it’s hard to say what’s native to a novel ecosystem like the Delta. Today’s Delta isn’t the Delta where Delta smelt evolved or where winter run Chinook salmon evolved, and these species are not well adapted to today’s Delta. Within this framework, guest species like the striped bass are as native to a novel ecosystem as anything else. This is not to devalue the biodiversity offered by native species–it must be protected as well. But it does mean that we shouldn’t devalue guest species in novel ecosystems just because they were not a part of the historic ecosystem.

This brings up the fourth and final theme: guest species may be better adapted for the current environment than native species. In places like the Delta, the habitat has been changed so much that species evolved for the historic Delta cannot survive without intense and ongoing human intervention. This is only going to get worse under climate change. A recent study of California fishes found that, under project climate scenarios, “[m]ost native fishes will suffer population declines and become more restricted in their distributions; some will likely be driven to extinction. . . . In contrast, most alien fishes will thrive, with some species increasing in abundance and range.”

This means we must think long and hard about removing guest species. If these species are the most likely to survive our future climate, removing them now in a bid for historical ecosystem re-creation is misguided and shortsighted. We could end up with nothing left to protect.

Karrigan Bork is a Visiting Assistant Professor with a joint appointment at the McGeorge School of Law and the Dept. of Geological & Environmental Sciences, both part of the University of the Pacific. He is also a visiting researcher at the UC Davis Center for Watershed Sciences. His research interests include environmental law, natural resources law, international law, and administrative law, focusing on the interplay of science and law. For more information visit his SSRN page.

Further reading

Karrigan Börk, Guest Species: Rethinking Our Approach to Biodiversity in the Anthropocene, 2018 Utah L. Rev. 169 (2018).

Moyle, PB, Jeffres CA, and Durand J. 2018. Resurrecting the Delta for desirable fishes. California WaterBlog.

Moyle PB et al. 2016. Understanding predation impacts on Delta native fishes. California WaterBlog.

Moyle PB and Bennett WA, 2011.  Striped Bass: the cure worse than the disease. California WaterBlog.

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4 Responses to Guest Species – What about the nonnative species we like?

  1. eacano says:

    I would add feral and household cats which decimate native bird species.

  2. Kieran Suckling says:

    State wildlife agencies drove many species extinct, purposefully poisoned hundred of miles of rivers to kill off native fish, and regularly violate both state and federal environmental laws. This often requires federal agencies to step in to enforce the Clean Water Act, list a species as endangered or require habitat mitigation under NEPA. Yet, you conclude that “federal oversight of state wildlife management breeds conflict.” No. The state’s harming of the environment, violating state and federal laws and ignoring its public trust responsibility is what bred the conflict.

    Your framing is not accidental or new. It is exactly what the coal industry has been saying about the EPA for decades (federal oversight breeds conflict by forcing us to protect water quality while the state looks the other way), what mining corporations have been saying about the Army Corps of Engineers for decades (that it creates conflicts by insisting on clean air standards that the states do not), and developers have been saying about the U.S. Fish and Wildlife Service for decades (that it creates conflict by requiring habitat mitigation for species which aren’t even protected by the states), and sweatshop operators have been saying about the Department of Labor for decades, and what gerrymandering state politicians have been saying about the Department of Justice for decades. Blaming those who enforce public health, safety and environmental laws for “creating conflict” instead of the lawbreakers is the classic regressive political gesture. Turns out Obama didn’t breed race conflict by getting elected president and the Fish and Wildlife Service didn’t breed endangered species conflict by telling ranchers to stop overgrazing our federal lands. The conflict was bred by those trashing the land and resentful of civil rights. The next time a cop pulls me over for speeding, I wave your essay and Exxon’s lobbying letters in her face and tell her she’s breeding conflict.

    Yes, some hunters enjoy shooting sheep in Palila habitat, but other hunters (and many nonhunters) oppose it. Your essay reinscibes another traditional regressive gesture by calling the former the public, the people, and treating the latter as bureaucratic intervenors. But that is slight of hand. They are all the public and the conflict is between competing public interests, not the public and bureaucrats.

    Arguing that we should keep harmful invasive species at high population levels because (some) people like them is not as your law review essay suggests, a democraticing gesture. Some people like coal mines. Many more liked slavery. A large minority of the nation likes marriage being limited to heterosexual couples. Many people like oil drilling. I’ll wager that more people like to spray neonictinoid pesticides on their lawns than like to bass fish and they spend more money doing it. In short, it is very weak public policy team to hinge arguments on the fact that some people like some things. Especially so you omit the fact that other people don’t like that thing.

    You describe the bass suit as a “bombshell” showing that the Endangered Species Act is out of date and unable to deal properly with invasive species. But the opposite is clearly true. The case was a dud, that never even got as far as a summary judgement ruling. And it collapsed precisely because the ESA’s future-thinking “best available science” standard properly forced the court to review and rely on the best science in making its early decisions. The bass case is actually an example of the ESA handling a complex invasive species issue quite well because of its purposefully designed flexibility to evolve as the best science evolves.

    Your law article invocation of Palila is a similar misfire. Feds breeding controversy? Long before any federal involvement or even the existence of the ESA, there was a huge conflict with state foresters and private loggers on one side, and hunters on the other. A compromise was negotiated resulting in the first attempt to fence sheep and goats out of part of the Palila’s habitat. Decades later, the fence was not maintained by the state causing farmers/ranchers to fight with hunters over the sheep and deer. (Yes farmers and ranchers are members of the public). Later still, the environmentally interested public demanded reforms because of native forest destruction and the Palila’s decline. Again all this was before federal or ESA involvement. The state agreed to fence sheep out of 25% of the area, but then failed to follow through as it had in the past, angering many Hawaiians. So Palila teaches us the environmental conflict is bred by some people deriving a benefit by harming the resources and environmental values important to other people. It was not the feds or the ESA which initiated the conflict on Mauna Kea.

    You argue that the Palila order to remove the exotic ungulates dangerously opened to door to a tidal wave of hunting management take lawsuits over introduced game animals. But Palila was decided in 1979–40 years ago. There was no tidal wave, not even a sneaker wave. The invocation of fear today is untenable. Palila teaches the exact opposite. The ESA was successfully used to hold the state’s feet to fire in a specific situation where it consistently failed over many decades to carry out it’s own promised actions which it said were necessary to protect the environment and settle divergent public interests. The intensity of the ungulate impact, the severe status of the Palila, the limitation to state land, the designation of critical habitat sustaining the legal argument, and the state’s specific history of failed promises made the case unlikely to spawn large numbers of replicant suits and in fact, that was the case. Not many similar suits were filed in the subsequent 40 years.

    The ESA worked as it should in both cases, though the outcome was very different. In both cases, voluminous scientific evidence was presented to, reviewed by, and formed the basis of the court’s ruling. The ESA requires this and the public interest benefits from it.

    The ESA has also reasonably, successfully and with great restraint been used to remove harmful invasive trout from streams needed to recover the endangered Gila trout, Apache trout, golden trout and other listed fish. The sky did not fall. State agencies did not collapse (indeed they helped). Fisherman did not self immolate (some opposed, others helped). The much exaggerated North American Wildlife Model continued in all its mythologized grandeur. Introduced trout still vastly exceed these natives in numbers and stream lengths. Recreationsl fishing continues. In short, the great crisis invoked by this essay is much to do about nothing. Academic pundits not withstanding, actual ecologists, conservationists, state and federal wildlife and habitat managers and environmentally minded hunters and fisher will continue for the most part to prioritize dealing with the greatest threat as to endangered species. This does not include a fantasized national jihad to remove all introduced game species from all areas. No special legislation or legislative exemptions are needed.

  3. Karrigan Bork says:

    Thanks for engaging on this issue. Your organization does some great work. Quick response on a couple of points:

    First, it’s clear that federal and state governments come into conflict pretty consistently over guest species. There are different ways to describe this situation: “The state’s harming of the environment, violating state and federal laws and ignoring its public trust responsibility is what bred the conflict” is one. Another would suggest federal overreach into areas of traditional state authority result in conflict. It’s also significant that this is state governments vs federal government, not federal governments regulating private interests. I think the right description is somewhere in the middle, albeit closer to your perspective. More to the point, it’s clear that when state efforts to manage wildlife but up against areas of federal interest, there will be fights that will complicate management efforts for both sides. That’s the take home.

    Second, I’m not basing a public policy argument on the fact that some people like some things, although in a democracy public opinion has to play a significant role. I’m merely recognizing that many guest species have strong and politically savvy support. That’s (in part) why a situation that should have been resolved a long time ago – exclusion of the goats from Palila habitat – has dragged on for 40 years, with goats still occupying the habitat. And that’s (in part) why removal of nonnative trout for native trout reintroductions takes so long and is so contentious. In some cases, public interest in guest species is certainly a valid consideration in determining how to manage those species. In nearly all cases, it has to be a consideration in the logistics of carrying out a given management decision. Interest groups don’t get a veto, but they are powerful voices.

    Third, I do argue that guest species are a significant issue for the ESA, but that doesn’t mean the ESA is out of date. Fear of lawsuits has impacted striped bass management in California for decades, and game management leaves many, probably most, states open to ESA suits. New legislation for the ESA isn’t feasible or necessary to address this issue, but administrative actions could both clarify liability and, as needed, permit potential take through the incidental take process. This would have the added benefit of mitigating the ongoing take by guest species, so native species would probably be better off under this scenario than under the current scenario, where we tend to ignore the impacts of the nonnative species we like. It’s a complicated issue, and pretending the impacts aren’t occurring doesn’t help.

    Generally, guest species make management more complicated and nuanced. In some cases, the right outcomes are easy to see (goat removal, removal of nonnative trout for native trout reintroduction), but even in those “easy” cases, the support for guest species makes implementation difficult and very protracted. The cases like striped bass in the Delta or earthworms or pheasant all over the place are much harder, both in terms of deciding what should be done and in carrying out those decisions.

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