ESR 33:193-209 (2017)  -  DOI: https://doi.org/10.3354/esr00806

Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill

Trent L. McDonald1,*, Fawn E. Hornsby1, Todd R. Speakman2, Eric S. Zolman2, Keith D. Mullin3, Carrie Sinclair3, Patricia E. Rosel4, Len Thomas5, Lori H. Schwacke

1Western EcoSystems Technology, Inc., Laramie, WY 82070, USA
2National Centers for Coastal Ocean Science, National Oceanic and Atmospheric Administration, Hollings Marine Laboratory, Charleston, SC 29412, USA
3National Marine Fisheries Service, Southeast Fisheries Science Center, Pascagoula, MS 39568, USA
4National Marine Fisheries Service, Southeast Fisheries Science Center, Lafayette, LA 70506, USA
5Centre for Research into Ecological and Environmental Modelling, University of St. Andrews, St. Andrews KY16 9LZ, UK
*Corresponding author:

ABSTRACT: To assess potential impacts of the Deepwater Horizon oil spill in April 2010, we conducted boat-based photo-identification surveys for common bottlenose dolphins Tursiops truncatus in Barataria Bay, Louisiana, USA (~230 km2, located 167 km WNW of the spill center). Crews logged 838 h of survey effort along pre-defined routes on 10 occasions between late June 2010 and early May 2014. We applied a previously unpublished spatial version of the robust design capture-recapture model to estimate survival and density. This model used photo locations to estimate density in the absence of study area boundaries and to separate mortality from permanent emigration. To estimate abundance, we applied density estimates to saltwater (salinity > ~8 ppt) areas of the bay where telemetry data suggested that dolphins reside. Annual dolphin survival varied between 0.80 and 0.85 (95% CIs varied from 0.77 to 0.90) over 3 yr following the Deepwater Horizon spill. In 2 non-oiled bays (in Florida and South Carolina), historic survival averages approximately 0.95. From June to November 2010, abundance increased from 1300 (95% CI ± ~130) to 3100 (95% CI ± ~400), then declined and remained between ~1600 and ~2400 individuals until spring 2013. In fall 2013 and spring 2014, abundance increased again to approximately 3100 individuals. Dolphin abundance prior to the spill was unknown, but we hypothesize that some dolphins moved out of the sampled area, probably northward into marshes, prior to initiation of our surveys in late June 2010, and later immigrated back into the sampled area.


KEY WORDS: Robust design · Photo-identification · Tursiops truncatus · Capture-recapture · Spatial-capture model


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Cite this article as: McDonald TL, Hornsby FE, Speakman TR, Zolman ES and others (2017) Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill. Endang Species Res 33:193-209. https://doi.org/10.3354/esr00806

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