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Survival, Density and Abundance of Common Bottlenose Dolphins in Barataria Bay (USA) Following the Deepwater Horizon Oil Spill

December 06, 2023

We conducted boat-based photo-identification surveys for common bottlenose dolphins Tursiops truncatus in Barataria Bay, Louisiana.

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 kilometers2, located 167 kilometer WNW of the spill center). Crews logged 838 hours 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 We applied a previously unpublished spatial version of the robust design capture-recapture model to estimate survival and density.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 parts per thousand) areas of the bay where telemetry data suggested that dolphins reside. Annual dolphin survival varied between 0.80 and 0.85 (95% Confidence Intervals varied from 0.77 to 0.90) over 3 years 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.

McDonald, T. L., F. E. Hornsby, T. R. Speakman, E. S. Zolman, K. D. Mullin, C. Sinclair, P. E. Rosel, L. Thomas, L. H. Schwacke. 2017. Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill. Endangered Species Research, 33, 193-209.


Last updated by Southeast Fisheries Science Center on 12/06/2023