Using Photo-Identification and Genetic Data to Examine Fine-Scale Population Structure of Common Bottlenose Dolphins (Tursiops truncatus) in the Estuarine Waters Surrounding Savannah, Georgia

Many marine mammal species exhibit complex patterns of population structure. Specifically, common bottlenose dolphin (Tursiops truncatus) populations in the southeastern United States display varying degrees of spatial overlap and residency, including some that have year-round site fidelity to localized bays, sounds, and estuaries. Evidence of resident estuarine animals along the U.S. Atlantic and Gulf of Mexico coastlines is supported through photo-identification and genetic studies, although, currently, few studies have integrated both methods. The purpose of this project was to couple long-term photo-identification data with spatial and genetic analyses to examine population structure of common bottlenose dolphins in northern Georgia. Genomic DNA was extracted from skin samples (n = 69) collected in the Northern Georgia/Southern South Carolina Estuarine System Stock, and a portion of the mitochondrial DNA control region was sequenced. To determine potential fine-scale geographic delineations within this stock, the study area was split into three regions: (1) north, (2) buffer, and (3) south. No significant genetic differentiation was found when regions were compared by only sample collection location. The sighting locations of sampled dolphins that had been seen >= 10 times between 2009 and 2017 (n = 45) were mapped in ArcMap, Version 10.2. In an analysis of dolphins with >= 10 sightings only, a significant difference in F-ST was found between the north vs buffer area (p = 0.0147). When dolphins with 10 sightings (n = 45) were assigned to the region where >= 50% of their sightings were located, a significant difference in F-ST was found between the north vs butter and north vs south regions (p = 0.0018 and p = 0.0164, respectively). The addition of spatial data revealed genetic division among, the three regions. Thus, the combination of photo-identification and genetic analyses used in this study may be useful in determining population structure in the future.