WASHINGTON— In January 2025 a paper published in Current Biology (Ghezelayagh et al. 2025) explained that genetic analysis demonstrated that snail darters (Percina tanasi) represented a population of the more widely distributed stargazing darter (Percina uranidea) and are no longer a valid species.
The snail darter was the species at the center of the Tellico Dam controversy that culminated in the U.S. Supreme Court’s Tennessee Valley Authority v. Hill decision in 1976, and the new paper has drawn attention from Republican politicians eager to roll back Endangered Species Act protections for imperiled wildlife.
Kierán Suckling, executive director of the Center for Biological Diversity, provided the following statement in response to this paper:
“Since 1973, the Endangered Species Act has required the use of the best available science to guide decisions about which species to protect. The available science in 1976, long before computers or genetic research for conservation even existed, made clear the snail darter was a valid species worthy of protection. Science, by definition, is updated as new information is tested. That includes our understanding of species’ taxonomy. It’s unethical for politicians to vilify the scientists who described the snail darter. And even if snail darters were merely a population of the stargazing darter, the original 1973 Endangered Species Act would still have been able to protect them as a matter of law.
“The Supreme Court itself noted the controversial nature of the snail darter’s status as a species, acknowledging that the work of Dr. David Etnier was published in the Proceedings of the Biological Society of Washington, and that the scientific merit and content of Dr. Etnier’s paper on the snail darter were reviewed by a panel from the Smithsonian Institution prior to publication. It’s a shame that a small number of individuals are ginning up a controversy where none exists, and this will now be exploited by cynical politicians to try to weaken protections across the board for this nation’s most imperiled wildlife.”
Taxonomy and Protection of the Stargazing Darter in Tennessee
The Ghezelayagh paper explains that there are five disjunct populations of the stargazing darter — the White River, Ouachita, River, Wabash River, Lower Mississippi River and the Tennessee River. The snail darter made up the population found within the Tennessee River.
The original, unamended Endangered Species Act of 1973 provided for the protection of “species” which at the time was defined to include “any subspecies of fish or wildlife or plants and any other group of fish or wildlife of the same species or smaller taxa in common spatial arrangement that interbreed when mature.” Similar to the current law, a species could be protected as “threatened” or “endangered” based on threats throughout all or a significant portion of the species’ range.
Without support or explanation, the Ghezelayagh paper states: “It is not clear if the level of distinctiveness of the snail darter would merit protection as either a subspecies or [distinct population segment].” However, the “distinct population segment” authority in the law was not added until 1978, five years after the snail darter was protected.
The Tennessee River population of the stargazing darter could have been protected as a “group…in common spatial arrangement.” Likewise, because the Tennessee River population could represent a “significant portion” of the range of the species writ large, the Tennessee population could have been protected via that legal mechanism as well. The authors’ conclusions about the distinct population segment authority’s applicability are simply ahistorical and demonstrate a failure to assess the stargazing darter’s conservation status through the lens of the original 1973 Act before it was amended.
Taxonomic Revisions and Reclassifications Under the Endangered Species Act
Since 1973, 21 species protected under the Endangered Species Act have been removed from the list of threatened and endangered species because new scientific information, often genetic analysis, indicated that the original listed entity was not a valid species or was merely a population of a larger, and more common species that was not threatened. Species have also been delisted because additional surveys of hard to detect species determined that they were more abundant than scientists first believed.
In other instances species that were listed as a single entity, such as least terns and clapper rails, were split into multiple species, each of which was protected as a distinct species under the law. In some situations widespread species including humpback whales and sea turtles were divided into multiple distinct population segments because this allowed for more targeted conservation to occur. Salmon runs are often protected as “evolutionarily significant units.” None of these reclassifications and revisions are unusual or demonstrate an abuse of the law’s mechanisms.
Throughout the listing review and after listing, multiple processes and comment periods are in place where taxonomy can be reviewed. The Endangered Species Act’s five-year-review process provides for periodic assessment of every species’ conservation status and allows for new scientific information to be brought forward, including to address new genetic and taxonomic research. During reviews for listing, the Center for Biological Diversity has withdrawn more than 100 previously petitioned species due to updated information on species’ taxonomy or status.
More broadly, taxonomy continues to be an active field of scientific work for biologists for nearly every major taxonomic group of species. In 1973 there were approximately 9,800 species of recognized birds in the world, while today there are nearly 11,000 recognized species. Similarly, in 1998 there were approximately 53,000 recognized fish species and subspecies in the world, while today there are more than 65,000.
While the overall trend has been an increase each year in the number of recognized species, scientists routinely also identify species whose status should no longer be accepted. A very small number of scientists have argued that taxonomists are biased and utilize the “conservation species concept” to further conservation of nonvalid species. However, there is no scientific support that the larger global trend toward more recognized species is driven by anything other than the normal scientific process.
Original Basis for the Snail Darter’s Status as a Species
As with all proposals to list species, the U.S. Fish and Wildlife Service provided a period of public comment on the snail darter. A dozen ichthyologists supported the taxonomic conclusions and status of the snail darter. To be extra cautious, the Service asked the Smithsonian to convene an independent scientific panel to review the taxonomy, which also concluded the snail darter was a valid species. Even Edward Raney, Ph.D., a leading ichthyologist from Cornell University hired by the Tennessee Valley Authority to support the dam’s construction, did not dispute the validity of the species.
Because the snail darter issue was so controversial, multiple scientific authorities including the Smithsonian examined the science underlying its basis as a species but were not able to contradict its status based on the conservation and scientific tools available at the time to taxonomists. Only with the addition of genetic data, further specimens for morphological comparison, and a comprehensive review of the darter populations were the Ghezelayagh authors able to determine the snail darter was a part of the stargazing darter. All of this information was not available 50 years ago.
In terms of morphological differences, Dr. Etnier recorded multiple distinctions of “snail darters” from stargazing darters including shorter and more rounded pectoral fins, shorter pelvic fins in males and females, a higher number of anal rays, lack of nuptial male tubercles on the pelvic spine and differences in the number of overlying lateral-line scales in both males and females. The original description of the snail darter reads as follows:
Most closely related to Percina uranidea (stargazing darter) but differing from that species in having shorter paired fins; a more robust body (interorbital width, width below origin of soft dorsal fin, and width below origin of third saddle). Dorsal saddles of Percina tanasi are wider than those of Percina uranidea from the Saline and Wabash river systems, and much wider than those of Percina uranidea from the White River system…
Thus the original scientists were aware that snail darters were similar to stargazing darters, but using the best available scientific techniques available in the 1970s, mainly morphological comparisons, were able to conclude at the time that the snail darter was a valid species.
Attempts to discount the work of these scientists — including a highly respected ichthyologist who is now deceased — and retroactively impugn their integrity is nothing more than sensationalism.
