Population Structure and Connectivity of Atlantic Nurse Sharks (Ginglymostoma cirratum) in the Bahamas and Outlying Areas

Authors

• Baylie A. Fadool, University of Nebraska-LincolnFollow

First Advisor

Rene Martin

Committee Members

Sarah Sonsthagen, Rebecca Varney

Date of this Version

5-2026

Document Type

Thesis

Citation

A thesis pesented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Natural Resource Sciences

Under the supervision of Professor Rene Martin

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Baylie A. Fadool. Used by permission

Abstract

Understanding animal ecosystem dynamics and behavior at the individual and population levels is essential for identifying life-history patterns and important areas for management and conservation. Marine fish species often face minimal geographic barriers to movement, but environmental (temperature, salinity, current) or intrinsic barriers (philopatry, site fidelity) can dictate gene flow. Atlantic nurse sharks (Ginglymostoma cirratum) are an International Union for Conservation of Nature (IUCN) listed ‘vulnerable’ species and present a unique opportunity to investigate patterns of population structure and connectivity in large-bodied sharks. They are benthic and display reproductive philopatry, with recent work suggesting they have the capacity for seasonal, large-scale movements. Combining acoustic telemetry and genomic methods, we investigate patterns of dispersal in individuals and between populations of nurse sharks. We used data from 20 nurse sharks tagged with acoustic transmitters from 2015–2017 in Bimini, The Bahamas. We additionally use tissue samples collected from 95 nurse sharks throughout four islands in The Bahamas and one atoll in Brazil from 1996–2020, performing double digest restriction site-associated DNA sequencing and multiple qualitative (fixation indices, heterozygosity, pairwise differentiation) and quantitative (clustering algorithms) metrics. Acoustic telemetry revealed that nurse sharks perform partial migration, with seasonal repeated migrations of moderately far distances and across international jurisdictions but show overwhelming site fidelity to Bimini. Our genomic analysis uncovered weak but significant population structure among regions, however, most of the genetic diversity occurred within samples. Nurse sharks also experienced a recent population expansion, leading to an excess of rare alleles that could be creating weak signatures of population differentiation and explaining the higher diversity within samples. We attribute their weak population structure to the strong reproductive philopatry of nurse sharks. In light of nurse sharks being wide-ranging and performing seasonal migrations, it is possible that reproducing migrants also contribute to the observed low genetic structure. Our data show that nurse sharks are more wide-ranging than previously understood and exhibit gene flow between populations. Since gene flow is relatively maintained with weak genetic structure, current management implementation throughout The Bahamas is likely providing sufficient coverage, minimizing the need for localized strategies.

Advisor: Rene Martin