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ESR 33:235-252 (2017)  -  DOI: https://doi.org/10.3354/esr00783

Assigning stranded bottlenose dolphins to source stocks using stable isotope ratios following the Deepwater Horizon oil spill

A. A. Hohn1,*, L. Thomas2, R. H. Carmichael3,4, J. Litz5, C. Clemons-Chevis6, S. F. Shippee7, C. Sinclair8, S. Smith9,12, T. R. Speakman10, M. C. Tumlin11, E. S. Zolman10

1National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 101 Pivers Island Rd., Beaufort, NC 28516, USA
2Centre for Research into Ecological and Environmental Modelling (CREEM), University of St Andrews, The Observatory, Buchanan Gardens, KY16 9LZ, UK
3Dauphin Island Sea Lab, Dauphin Island, AL 36528, USA
4University of South Alabama, Mobile, AL 36688, USA
5National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Key Dr., Miami, FL 33149, USA
6Institute for Marine Mammal Studies, PO Box 207, Gulfport, MS 39502, USA
7Marine Wildlife Response, 1557 Highway 98 West, Mary Esther, FL 32569, USA
8National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, 3209 Frederic St., Pascagoula, MS 39567, USA
9Audubon Aquarium of the Americas, 1 Canal Street, New Orleans, LA 70124, USA
10National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Hollings Marine Laboratory, 331 Fort Johnson, Charleston, SC 29412, USA
11Louisiana Department of Wildlife and Fisheries, 2000 Quail Drive, Baton Rouge, LA, 70898, USA
12Present address: Amazon River Dolphin Conservation Foundation, 805 Hidalgo Street, New Orleans, LA 70124, USA
*Corresponding author:

ABSTRACT: The potential for stranded dolphins to serve as a tool for monitoring free-ranging populations would be enhanced if their stocks of origin were known. We used stable isotopes of carbon, nitrogen, and sulfur from skin to assign stranded bottlenose dolphins Tursiops truncatus to different habitats, as a proxy for stocks (demographically independent populations), following the Deepwater Horizon oil spill. Model results from biopsy samples collected from dolphins from known habitats (n = 205) resulted in an 80.5% probability of correct assignment. These results were applied to data from stranded dolphins (n = 217), resulting in predicted assignment probabilities of 0.473, 0.172, and 0.355 to Estuarine, Barrier Island (BI), and Coastal stocks, respectively. Differences were found west and east of the Mississippi River, with more Coastal dolphins stranding in western Louisiana and more Estuarine dolphins stranding in Mississippi. Within the Estuarine East Stock, 2 groups were identified, one predominantly associated with Mississippi and Alabama estuaries and another with western Florida. δ15N values were higher in stranded samples for both Estuarine and BI stocks, potentially indicating nutritional stress. High probabilities of correct assignment of the biopsy samples indicate predictable variation in stable isotopes and fidelity to habitat. The power of δ34S to discriminate habitats relative to salinity was essential. Stable isotopes may provide guidance regarding where additional testing is warranted to confirm demographic independence and aid in determining the source habitat of stranded dolphins, thus increasing the value of biological data collected from stranded individuals.


KEY WORDS: Carbon · Nitrogen · Sulfur · Tursiops truncatus · Stock structure · Gulf of Mexico


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Cite this article as: Hohn AA, Thomas L, Carmichael RH, Litz J and others (2017) Assigning stranded bottlenose dolphins to source stocks using stable isotope ratios following the Deepwater Horizon oil spill. Endang Species Res 33:235-252. https://doi.org/10.3354/esr00783

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Published in ESR Vol. 33. Online publication date: January 31, 2017
Print ISSN: 1863-5407; Online ISSN: 1613-4796
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