Where were they from? Modelling the source stock of dolphins stranded after the Deepwater Horizon oil spill using genetic and stable isotope data

L. Thomas; C. G. Booth; P. E. Rosel; A. Hohn; J. Litz; L. H. Schwacke

doi:10.3354/esr00754

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ESR 33:253-264 (2017) - DOI: https://doi.org/10.3354/esr00754

Where were they from? Modelling the source stock of dolphins stranded after the Deepwater Horizon oil spill using genetic and stable isotope data

L. Thomas^1,*, C. G. Booth², P. E. Rosel³, A. Hohn⁴, J. Litz⁵, L. H. Schwacke⁶

¹Centre for Research into Ecological and Environmental Modelling (CREEM), University of St Andrews, The Observatory, Buchanan Gardens, St Andrews KY16 9LZ, UK
²SMRU Consulting Europe, New Technology Centre, North Haugh, St Andrews KY16 9SR, UK
³National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 646 Cajundome Blvd., Lafayette, LA 70506, USA
⁴National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 101 Pivers Island Rd, Beaufort, NC 28516, USA
⁵National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Beach Drive, Miami, FL 33149, USA
⁶National Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science, 331 Fort Johnson Road, Charleston, SC 29412, USA

*Corresponding author: len.thomas@st-andrews.ac.uk

ABSTRACT: Understanding the source stock of common bottlenose dolphins Tursiops truncatus that stranded in the northern Gulf of Mexico subsequent to the Deepwater Horizon oil spill was essential to accurately quantify injury and apportion individuals to the appropriate stock. The aim of this study, part of the Natural Resource Damage Assessment (NRDA), was to estimate the proportion of the 932 recorded strandings between May 2010 and June 2014 that came from coastal versus bay, sound and estuary (BSE) stocks. Four sources of relevant information were available on overlapping subsets totaling 336 (39%) of the strandings: genetic stock assignment, stable isotope ratios, photo-ID and individual genetic-ID. We developed a hierarchical Bayesian model for combining these sources that weighted each data source for each stranding according to a measure of estimated precision: the effective sample size (ESS). The photo- and genetic-ID data were limited and considered to potentially introduce biases, so these data sources were excluded from analyses used in the NRDA. Estimates were calculated separately in 3 regions: East (of the Mississippi outflow), West (of the Mississippi outflow through Vermilion Bay, Louisiana) and Western Louisiana (west of Vermilion Bay to the Texas-Louisiana border); the estimated proportions of coastal strandings were, respectively 0.215 (95% CI: 0.169-0.263), 0.016 (0.036-0.099) and 0.622 (0.487-0.803). This method represents a general approach for integrating multiple sources of information that have differing uncertainties.

KEY WORDS: Genetic assignment · Stable isotope ratios · Bayesian hierarchical model · Data integration · Deepwater Horizon · Stranding

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Cite this article as: Thomas L, Booth CG, Rosel PE, Hohn A, Litz J, Schwacke LH (2017) Where were they from? Modelling the source stock of dolphins stranded after the Deepwater Horizon oil spill using genetic and stable isotope data. Endang Species Res 33:253-264. https://doi.org/10.3354/esr00754

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ESR 33:253-264 (2017) - DOI: https://doi.org/10.3354/esr00754

Where were they from? Modelling the source stock of dolphins stranded after the Deepwater Horizon oil spill using genetic and stable isotope data

L. Thomas1,*, C. G. Booth2, P. E. Rosel3, A. Hohn4, J. Litz5, L. H. Schwacke6

L. Thomas^1,*, C. G. Booth², P. E. Rosel³, A. Hohn⁴, J. Litz⁵, L. H. Schwacke⁶