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ESR 33:265-279 (2017)  -  DOI: https://doi.org/10.3354/esr00777

Quantifying injury to common bottlenose dolphins from the Deepwater Horizon oil spill using an age-, sex- and class-structured population model

Lori H. Schwacke1,8,*, Len Thomas2, Randall S. Wells3, Wayne E. McFee1, Aleta A. Hohn4, Keith D. Mullin5, Eric S. Zolman1, Brian M. Quigley1, Teri K. Rowles6, John H. Schwacke7

1National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Charleston, South Carolina 29412, USA
2Centre for Research into Ecological and Environmental Modelling (CREEM), University of St Andrews, The Observatory, Buchanan Gardens KY16 9LZ, UK
3Chicago Zoological Society, c/o Mote Marine Laboratory, Sarasota, Florida 34236, USA
4National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, Beaufort, North Carolina 28516, USA
5National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, Pascagoula, Mississippi 39568, USA
6National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Office of Protected Resources, Silver Spring, Maryland 20910, USA
7Scientific Research Corporation, Charleston, South Carolina 29406, USA
8Present address: National Marine Mammal Foundation, San Diego, California 29106, USA
*Corresponding author:

ABSTRACT: Field studies documented increased mortality, adverse health effects, and reproductive failure in common bottlenose dolphins Tursiops truncatus following the Deepwater Horizon (DWH) oil spill. In order to determine the appropriate type and amount of restoration needed to compensate for losses, the overall extent of injuries to dolphins had to be quantified. Simply counting dead individuals does not consider long-term impacts to populations, such as the loss of future reproductive potential from mortality of females, or the chronic health effects that continue to compromise survival long after acute effects subside. Therefore, we constructed a sex- and age-structured model of population growth and included additional class structure to represent dolphins exposed and unexposed to DWH oil. The model was applied for multiple stocks to predict injured population trajectories using estimates of post-spill survival and reproductive rates. Injured trajectories were compared to baseline trajectories that were expected had the DWH incident not occurred. Two principal measures of injury were computed: (1) lost cetacean years (LCY); the difference between baseline and injured population size, summed over the modeled time period, and (2) time to recovery; the number of years for the stock to recover to within 95% of baseline. For the dolphin stock in Barataria Bay, Louisiana, the estimated LCY was substantial: 30347 LCY (95% CI: 11511 to 89746). Estimated time to recovery was 39 yr (95% CI: 24 to 80). Similar recovery timelines were predicted for stocks in the Mississippi River Delta, Mississippi Sound, Mobile Bay and the Northern Coastal Stock.


KEY WORDS: Population model · Monte Carlo analysis · Survival · Density dependence · Bayesian model · Deepwater Horizon · Impact assessment · Cetacean


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Cite this article as: Schwacke LH, Thomas L, Wells RS, McFee WE and others (2017) Quantifying injury to common bottlenose dolphins from the Deepwater Horizon oil spill using an age-, sex- and class-structured population model. Endang Species Res 33:265-279. https://doi.org/10.3354/esr00777

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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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