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.
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:
- federal oversight of state wildlife management breeds conflict;
- people love their guest species, which increases conflicts;
- guest species can eventually become part of the local ecosystem; and
- 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.
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.
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.
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.