In the aftermath of the Deepwater Horizon (DWH) catastrophe, impacts to bottlenose dolphins in heavily oiled coastal areas of the northern Gulf of Mexico were well documented. Necropsies of the recovered carcasses and studies of live dolphins within the DWH oil spill footprint confirmed lung injury and adrenal gland lesions consistent with known effects of oil or petroleum-associated compounds. In addition, a high incidence of reproductive failure was concluded from a lack of calves being observed during monitoring surveys of pregnant dolphins. Although the exact mechanism of reproductive failure has not be determined to date, proposed factors include compromised maternal health (specifically, pulmonary disease), direct oil-related toxic effects to the reproductive system, complications related to adrenal system dysfunction, and immune system perturbations leading to an increased susceptibility to reproductive pathogens. The underlying factors for the observed reproductive impairment are a critical but lingering research question. Addressing this question is essential to understand the process for bottlenose dolphin recovery specific to the DWH oil spill, and also to assess population risk and predict recovery trajectories for future spill events involving dolphins or other less wellstudied cetaceans.
In response to the GOMRI RFP-V environmental effects and science of ecosystem recovery theme, the overall goal of this project will be to investigate direct and indirect factors involved in the reproductive impairment observed in bottlenose dolphins following the DWH oil spill in order to better understand the process for population recovery. Much can be learned from Gulf dolphin populations such as those in Barataria Bay that are still experiencing reproductive impacts five years post-spill, but to do so will require employment of new diagnostic approaches. This research project will adapt and test cuttingedge medical technologies for evaluating potential reproductive system disorders and then integrate those technologies for dolphin capture-release field studies in Barataria Bay. Recent advances in diagnostic ultrasonography for cetaceans developed by the NMMF were adapted for field studies and applied in recent Gulf dolphin studies (2010-2014) to identify manifestations of pulmonary disease. This project will expand the ultrasonographic techniques and add new medical diagnostics for identifying fetal/placental abnormalities and maternal disease conditions that are likely to result in a negative outcome. In addition, conditions such as lung and adrenal gland disease that were described in dolphins from Barataria Bay following the DWH spill will be assessed to determine trends of disease recovery and potential association with reproductive outcome.
Understanding varying mechanisms of reproductive failure purely through study of a wild population is hindered by the impracticality of re-sampling specific individuals over the course of a pregnancy. Therefore, this project includes both retrospective (banked samples from successful and failed pregnancies) and prospective sampling of dolphins from the Navy’s Marine Mammal Program (>70 bottlenose dolphins) to develop insight into diagnostic indicators and their change over the course of a pregnancy in relation to reproductive outcome. The Navy population has been well studied for over 40 years, translating into significant contributions to marine mammal conservation and science, specifically through basic physiology research, diagnostic technique development, and case-control investigations of disease. In addition to the evaluations of live dolphins, the project will characterize disease states from recovered dolphin carcasses near Barataria Bay, as well as perinate (near birth) carcasses from Navy dolphins to assess trends in fetal distress, in utero infections and fetal characteristics.
Although the Barataria Bay and other nearshore dolphins were certainly not the only cetacean species exposed to DWH oil, nor likely the only populations affected, their distribution in relatively shallow coastal waters and their small size relative to other continental shelf and pelagic species makes them the most accessible cetaceans to study oil-spill related health and reproductive effects. They also provide an opportunity to evaluate change in disease prevalence that indicates recovery from such effects over time. The paired studies using the Barataria Bay and Navy dolphin populations will not only provide a mechanism to refine and validate new and innovative diagnostics, but also lend additional insight into the progression of disease that increases the risk of a negative reproductive outcome.
Project Research Overview (2016):
An overview of the proposed research activities from the GoMRI 2016 Meeting in Tampa.
Direct link to the Research Overview presentation.