ST. PETERSBURG, Fla.— In a formal peer-reviewed letter published today in Global Ecology and Conservation, experts in modeling and turtle biology detailed several errors in a population viability model that led to a significant overestimate of future gopher tortoise populations. The flawed model was used by the U.S. Fish and Wildlife Service to deny federal Endangered Species Act protections to the tortoises across most of their range in 2022.

Using a corrected model, the experts predict that less than 1% of tortoises will persist by the year 2100. By comparison, the flawed model the Service relied on to deny protections predicted roughly 67% would persist in the same time period.

“The previous model was far too flawed to use as a basis for decision making,” said Kevin Shoemaker, Ph.D., a professor of population ecology with expertise in using conservation simulation models and co-author of the letter. “I hope the Service does the right thing and re-evaluates their decision. In the meantime, researchers should move quickly to develop a more realistic model to support conservation decisions for this ecologically important species.”

“When we examined the simulated metapopulations one at a time, we realized that some of them were growing at a completely unrealistic rate,” said Kevin Loope, Ph.D., a research scientist who studies the conservation biology of gopher tortoises and co-author of the letter. “Hopefully the Service will re-evaluate their decision in light of predictions from an updated model. This case highlights the critical need for greater scrutiny of complex models when they are applied to important conservation decisions. The standard peer review process may not be sufficient in such cases, and small errors can have large effects.”

The publication explains that errors in the original gopher tortoise model led to much larger projected population sizes and lower risk of local extinctions in the future. Wildlife officials relied on the model’s mistaken overestimate when they decided gopher tortoises would be safe from extinction.

The letter also explains that an error in the way the model accounted for movement of gopher tortoises among habitat patches produced an inadvertent positive feedback loop, meaning that some simulated populations grew much faster than is biologically possible. Another error in the model inadvertently accelerated the rate of sexual maturation of juvenile gopher tortoises, which further contributed to the inflated population growth predictions.

“Given this model’s serious errors there’s no question that the Fish and Wildlife Service has to reconsider its decision to deny gopher tortoises endangered species protections,” said Ragan Whitlock, a Florida-based attorney at the Center for Biological Diversity. “The Endangered Species Act is so successful at recovering species because it requires wildlife officials to base decisions on the best science. There’s no exception for the gopher tortoise.”

“Demographic models are powerful predictive tools for wildlife management decisions, but it’s critical that they be constructed correctly and that the parameters are based on sound scientific data. Unfortunately, the original model that was used to predict the future survival of gopher tortoise populations was significantly flawed and resulted in an erroneous decision by the Service,” said Matthew Aresco, Ph.D., biologist and board member at Nokuse Education, Inc. “The Service should now re-evaluate its listing decision. Clearly, the corrected model results demonstrate that gopher tortoise populations are in deep trouble and warrant federal protection.”

In 2022 the Service denied federal Endangered Species Act protections to the eastern population of gopher tortoises in Florida, Georgia, South Carolina and most of Alabama. In 2023 the Center and Nokuse Education, Inc., sued the Service, arguing that the decision was arbitrary and departed from the best available science about the gopher tortoise’s status and threats. In the lawsuit, the conservation organizations highlighted significant flaws in the gopher tortoise population model that the Service relied upon.

Gopher tortoises in limited parts of Louisiana, Mississippi and western Alabama remained protected under the federal Endangered Species Act. Those in the eastern portion of their range have needed and been waiting for federal protection since 1982.

Gopher tortoises have shovel-like front legs and strong, thick back legs that help them dig deep burrows that more than 360 other species use. Gopher tortoise burrows are considered key features in the large, unfragmented upland ecosystems these communities of wild animals need to survive.