What is a chub, really?

In Arizona, three native chub species were reclassified as one, raising concerns about the management of the species.


In the rivers that wend through the Southwest swim three species of chub, a silvery native fish. When researchers encounter one in the quiet backwaters of the Colorado River Basin, though, they’re hard pressed to tell them apart. Is it the olive-gray roundtail darting around? Or if it’s a little chubbier, maybe that’s a headwater chub? Or perhaps it’s more portly than chubby, a bit darker? That might be the Gila chub. “Our department has always struggled to tell the difference between the three fish,” says Julie Carter, statewide native aquatics program supervisor of the Arizona Game and Fish Department.

But in September, the Joint Committee on the Names of Fishes, the eminent group on fish nomenclature, declared that the three species are actually one – the roundtail. What’s in a name? Potentially the very survival of the species, say ichthyologists who are resisting the decision. Critics of the reclassification say it could further imperil these three — or singular — species by tinkering with their status under the Endangered Species Act and potentially weakening their protections.

The Gila chub is a federally endangered species. It's now grouped with the roundtail chub, which is not listed.
Brian Gratwicke/Flickr user

In 2015, the Arizona Game and Fish Department requested the joint committee consider the case in hopes of finding a resolution to the decades-long debate. “The species has a troubled taxonomic history,” says Tom Dowling, a researcher at Wayne State University in Detroit, Michigan, who has studied the Gila complex of species since 1988. The movement of tectonic plates in the western U.S. shaped the physical features of the three fish populations, found in the Colorado River Basin, over the course of millions of years, first isolating the populations, then reuniting them before they had lost the ability to interbreed. Through the decades since they were first documented in the 1800s, scientists have made the case that the three exhibit enough differences to be their own species. But the latest decision, which looked at their genetic makeup, overturned that. The hope is this reclassification will make it easier for managers to identify them in the field. One study by the department found that observers could correctly classify the three fish just 54 percent of the time.

This sort of dispute isn’t new to Larry Page, chair of the Joint Committee on the Names of Fishes, a part of the American Fisheries Society and American Society of Ichthyologists and Herpetologists. Thousands of fish have been classified as their own species more than once. By looking at genetic information and species literature, the committee can whittle down which fish populations are duplicates and which merit their own species designation. For example, 24,993 species names of fish have been eliminated from the Catalog of Fishes in the last 25 years. In the case of the three Arizona chub species, Page says there were no genetic markings that indicate they deserve separate species labels; the fish breed with each other and the morphological differences are subtle.

But Dowling worries that this decision will have negative impacts on their genetic diversity by lumping them together as one, without taking into account their different lineages. In September, Dowling and two other ichthyologists wrote a letter to the U.S. Fish and Wildlife Service about their concerns, arguing that there was no new evidence in the past eight years that contradicted previous findings supporting separate species. The literature that the committee referred to included two unpublished, non-peer-reviewed studies. Dowling says he has concerns about the broader implications of the decision on other species if scientific literature can be used to make management decisions that have not been peer-reviewed or made publicly accessible. “This taxonomic dispute is not simply an academic exercise of whether to lump or split taxa,” the scientists wrote. “Because the decision has enormous implications for the conservation of imperiled species.”

Still, in the short term, little will likely change in how the fish are managed, Carter of AZGFD says. The department will keep managing the chubs under their existing state conservation agreements until the USFWS makes a decision on their respective listing status, including removing nonnative competitors and reintroducing the chubs to their historic ranges. After the USFWS listing decision, the department will continue to keep track of their lineages to ensure genetic diversity. “It’s not us throwing fish out willy nilly on the landscape,” Carter says.

It’s not clear whether the decision will affect the biggest factor in how the Gila, roundtail and headwater are managed: whether they are listed under the Endangered Species Act. The Gila, which inhabits just 15 percent of its historic range, was federally listed as endangered in 2005, the same year its fellow chubs, the roundtail and headwater, were found to merit protection. Eleven years later, USFWS still hasn’t finalized their status. Following the committee’s ruling, they pushed out their decision another six months, until April 17, 2017. At this point, the USFWS could ignore the reclassification and list the roundtail and headwaters as if they were still separate species, and reevaluate the Gila’s endangered status. Or they could lump them altogether as the roundtail chub and, if someone petitions them to do so, reassess their designation as one species.

In the meantime, the fish will remain in limbo, their future resting on a simple question: What’s in a name?

Anna V. Smith is an editorial intern at High Country News. She tweets

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