Sarah Toepfer

Date of Award


Degree Type

Honors College Thesis

Academic Program

Marine Biology BS


Biological Sciences

First Advisor

Nicole M. Phillips, Ph.D.

Advisor Department

Biological Sciences


Rhino-rays are the most threatened group of elasmobranchs, having experienced widespread declines due to mortalities in fisheries and habitat degradation. Within the Western Central Atlantic, there are two extant species of Rhino-rays, the Critically Endangered Smalltooth Sawfish, Pristis pectinata, and the Vulnerable Freckled Guitarfish, Pseudobatos lentiginosus. Although there is research committed to P. pectinata in this region, less is known about the distribution status of P. lentiginosus. Over the past 50 years, P. lentiginosus have undergone a presumed range contraction in U.S. waters; once found from North Carolina to Texas, and historically common in the north central Gulf of Mexico, they are now only abundant in Florida. Their occurrence in the north-central Gulf of Mexico remains uncertain, and they have not been sighted in the Mississippi Sound in 15 years. Therefore, a highly sensitive, species-specific Droplet Digital™ PCR environmental DNA (eDNA) assay was designed to detect the presence of this species, targeting a 174 base pair portion of the mitochondrial 16S rRNA gene. The assay detects DNA from only P. lentiginosus, and not from other co-occurring closely related species. This tool can be used in future eDNA surveys across the northern Gulf of Mexico and Western Central Atlantic to inform the current distribution of this threatened species and implement conservation action.