Doctor of Philosophy (PhD)


Renewable Natural Resources

Document Type



The small population sizes characteristic of many imperiled species means that they are vulnerable to both demographic and genetic extinction threats. Responses to these threats (e.g., population trends, genetic diversity estimates) are often difficult to obtain, but critical for conservation. Thus, researchers studying imperiled species may have to consult multiple data sources, collaborate with a wide variety of stakeholders, or ask new questions about previously collected data. I used this approach to understand more about the United States (U.S.) population of Pristis pectinata, an endangered elasmobranch that has declined up to 95% due to habitat loss and bycatch in commercial and recreational fisheries. First, I examined historical specimens from natural history and private collections originating throughout the former range in U.S. waters to identify temporal shifts in age class distribution and changes in maximum size. Based on the metadata and morphological measurements associated with these specimens I identified historical nursery areas and a decrease in maximum size over time. With genetic samples from these specimens, I was able to determine that the historical population was panmictic, had high genetic diversity, and began declining in the U.S. during the 1930s. Comparing these historical results to contemporary data, I show that P. pectinata, though still a small population, continues to retain genetic diversity over two recent generations and is showing signs of recovery. Finally, using genotypes from siblings to reconstruct parental genotypes, I determined that mature, female P. pectinata are regionally philopatric and rarely switch parturition sites. Taken together, these results can be used to guide restoration of previously occupied habitat, to facilitate population expansion, and to provide context for recovery estimates, all of which will be important for ensuring P. pectinata persistence into the future.

Committee Chair

Taylor, Sabrina S.