Island University Researchers Use Cutting-Edge Methods to Study DNA of Endangered Smalltooth Sawfish

CORPUS CHRISTI, Texas — Elasmobranchs are fishes that can be organized into two groups, one including sharks and the other including skates, rays, and sawfishes. Sawfishes are mythical in appearance, with long flattened bodies and fins, a shark-like tail, and fully grown adults can reach up to 18 feet in length. But their most distinctive feature is a flat, sword-like “nose” (properly called a rostrum) with small, densely packed rows of teeth lining the edges, resembling a saw. It’s hard to believe an animal as peculiar as the smalltooth sawfish exists and very few people have seen this endangered species in the wild.

The Marine Genomics Lab, located on the campus of Texas A&M University-Corpus Christi, has received a $376,132 grant over three years from the Shark Conservation Fund to use the latest DNA sequencing technologies to estimate the population size of the endangered smalltooth sawfish. The lab operates under the direction of Dr. David Portnoy, TAMU-CC Associate Professor and Marine Biology Graduate Program Coordinator; Dr. Dominic Swift ’22, a TAMU-CC Post-Doctoral Researcher in Portnoy’s lab is the lead researcher on the project.

“Smalltooth sawfish are fantastically beautiful animals,” Swift said. “I often think ‘How is this a real creature and not something from a fairy tale?’ They just look incredible!”

According to Swift, the smalltooth sawfish was once common in the warm shallow waters along the southeastern coast of the United States, with a vast range from North Carolina to Texas and as far south as Uruguay along the eastern coast of South America. Today, in the United States, they can be reliably found only in one area of southwest Florida, around Everglades National Park, as their numbers have severely declined due to fishing pressure and habitat loss. In 2003, the smalltooth sawfish became the first elasmobranch and native marine fish to receive federal protection under the Endangered Species Act (ESA).

Upon receiving the designation, the National Oceanic and Atmospheric Administration (NOAA) convened the Smalltooth Sawfish Recovery Team to build knowledge of the species, identify the most severe threats, and implement specific conservation actions to counter those threats.

“When a species is listed on the ESA, strict measures are put in place that impact the public, such as regulations around fishing,” Swift said. “A lot of effort goes into this, and you want to make sure that these conservation actions are actually helping to recover species.”

According to Swift, the decision to delist or downlist the smalltooth sawfish from “endangered” to “threatened” requires reliable estimates of their population size. Thankfully, the Smalltooth Sawfish Recovery Team has been collecting sample tissues from captured sawfish for the last 20 years and will be sharing these with TAMU-CC. Swift and the team in the Marine Genomics Lab will then use DNA extracted from the material to assess changes in smalltooth sawfish abundance.

Swift is hopeful that the project will show how conservation and management strategies can work to help an endangered species recover, and how cutting-edge science can be used to monitor that recovery.

“We can extract high-quality genomic DNA from these tissues,” Swift said. “This can be used to examine DNA sequences across the entire genome and identify kin relationships among smalltooth sawfish, such as parents and offspring, full and half siblings, and even cousins. We can then leverage these relationships to estimate population sizes at different points in time.”

Swift credits Portnoy, his mentor, for helping him develop this research and secure funding from the Shark Conservation Fund.

“Generating and analyzing the data needed for this project requires specialist skills which I’ve learned in Dr. Portnoy’s lab,” Swift said. “We also have specialized equipment to do the molecular analyses and the computing power to facilitate the data analysis. Dr. Portnoy is a great representative of the faculty here at TAMU-CC and his lab is a good demonstration of what the university can do in nurturing early-career researchers like me.”

Note: This work was made possible through the support of the Shark Conservation Fund, a sponsored project of the Rockefeller Philanthropy Advisors.