Assessing common bottlenose dolphin (Tursiops truncatus) population structure in Mississippi Sound and coastal waters of the north central Gulf of Mexico

Abstract

Population structure of highly mobile marine organisms can be complex and difficult to study, but it is important to understand how populations partition themselves within their environment for accurate assessment of both natural and anthropogenic impacts and successful management. The 2010 Deepwater Horizon oil spill negatively impacted common bottlenose dolphins (Tursiops truncatus) within Mississippi Sound and the surrounding north central Gulf of Mexico (GOMx); however, little was known about their underlying population structure in these waters. Thus, it was unclear how many demographically independent populations were affected by the spill. Common bottlenose dolphin samples were collected throughout inshore waters of Mississippi Sound and coastal waters of the north‐central GOMx. Mitochondrial DNA control region sequence data and 19 nuclear microsatellite loci were analysed to determine how many populations are present and characterize their range throughout these waters. Bayesian clustering and migration analyses identified two genetically distinct and demographically independent populations: one predominantly inhabiting Mississippi Sound and adjacent coastal waters, and a second population extending generally from offshore of Mobile Bay, Alabama, east along the Florida Panhandle. Neither of these populations align with the currently delineated management stocks previously used to estimate impacts from the oil spill on common bottlenose dolphins in this portion of the GOMx. These results suggest that revisions may be necessary so that management stocks accurately represent the demographically independent populations present in these waters. Furthermore, better comprehension of underlying population structure will enhance impact assessments on common bottlenose dolphins and provide more appropriate baseline data to support future restoration and conservation objectives.

Patterns of association and distribution of estuarine-resident common bottlenose dolphins (Tursiops truncatus) in North Carolina, USA

“…Spatial segregation often occurs in socially or genetically structured groups of bottlenose dolphins [ 91 ]. Spatial segregation in common and Indo-Pacific bottlenose dolphins has been identified within estuarine systems, embayments, or lagoons [e.g., 7 , 11 , 12 , 82 , 87 , 91 , 93 , 97 – 100 ], between or among estuarine and coastal groups [e.g., 8 , 14 , 84 , 99 – 104 ], as well as in coastal open-water areas [ 9 , 94 , 104 ]. The spatial segregation often reflects site fidelity and occurs despite the lack of physical barriers to movements [e.g., 7 , 88 , 94 , 100 , 105 ].…”

Population Dynamics Reveal a Core Community of the Common Bottlenose Dolphin (Tursiops truncatus) in Open Waters of the South-Western Gulf of Mexico

“…Population structure of highly mobile marine organisms can be complex and difficult to study, but it is important to understand how individuals within a population partition their environment, in order to better address conservation challenges (Vollmer et al, 2021). In this regard, recent advancements in the implementation of standardized site fidelity indexes (Tschopp et al, 2018) and considerations on residency patterns when studying cetacean population dynamics (e.g., Zanardo et al, 2016;Hunt et al, 2017;Passadore et al, 2017;Schleimer et al, 2019;Carlucci et al, 2020;Haughey et al, 2020) provide improved methodological tools for dealing with heterogeneity in capture or survival probabilities inherent to the dynamics of social species with fission-fusion societies such as bottlenose dolphins (Connor et al, 2000).…”

Fine‐scale social and genetic structure of common bottlenose dolphins (Tursiops truncatus) in the Barataria Basin, Louisiana, USA

“…For example, using photo‐ID data, Mazzoil et al (2008) identified three communities of dolphins within the Indian River Lagoon of Florida, but only two genetic clusters were differentiated by Richards et al (2013) using microsatellite data. Furthermore, analysis of telemetry and photo‐ID data of dolphins inhabiting Mississippi Sound, Mississippi/Alabama in the northern Gulf of Mexico (Mullin et al, 2017) identified at least two social groups but microsatellite data supported only a single population (Vollmer et al, 2021). The fission–fusion nature of dolphin societies might also explain why more social than genetic groups were found in the Barataria Basin.…”

“…Samples were genotyped at 43 nuclear polymorphic microsatellite loci previously optimized for T. truncatus (Rosel, Hansen & Hohn, 2009; Rosel et al, 2017; Vollmer et al, 2021; see Table S1). Modifications to original primer sequences were made for D08, DlrFCB12, EV94 and MK8 (Rosel et al, 2017; Vollmer & Rosel, 2017; Vollmer et al, 2021).…”

“…Samples were genotyped at 43 nuclear polymorphic microsatellite loci previously optimized for T. truncatus (Rosel, Hansen & Hohn, 2009; Rosel et al, 2017; Vollmer et al, 2021; see Table S1). Modifications to original primer sequences were made for D08, DlrFCB12, EV94 and MK8 (Rosel et al, 2017; Vollmer & Rosel, 2017; Vollmer et al, 2021). Excluding MK6, the reverse primer of each microsatellite locus or the forward primer of D22 was PIGtailed as described in Brownstein, Carpten & Smith (1996) to reduce one base pair stutter.…”