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 comparative studies of live dolphins within the DWH oil spill footprint vs. those from reference sites such as Sarasota Bay 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 – only 20% of documented pregnancies in Barataria Bay resulted in observed live calves, as compared to 83% for the reference population in Sarasota Bay.
Although the exact mechanism of reproductive failure has not yet been determined, proposed factors include compromised maternal health (specifically, lung 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-well-studied cetaceans.
With support through the Gulf of Mexico Research Initiative environmental effects and science of ecosystem recovery theme, we initiated a multi-year project in 2016. The project is adapting and testing cutting edge medical technologies for evaluating potential reproductive system disorders, and integrating these technologies for dolphin capture-release health assessments 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 lung disease. This project is expanding the ultrasonographic techniques and adding 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 are continuing to be assessed to determine trends of disease recovery and potential association with reproductive outcome. During July 2016, 38 dolphins were sampled and examined in Barataria Bay. Ten of these received satellite-linked transmitters, and these are showing a continuing strong pattern of local residency to Barataria Bay and vicinity.
The project also involves retrospective and prospective analysis of samples from the Navy’s Marine Mammal Program to develop insight into diagnostic indicators and their change over the course of a pregnancy in relation to reproductive outcome. In addition, the project is also characterizing disease states from dolphin carcasses recovered near Barataria Bay in order 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 or populations exposed to DWH oil, their coastal, shallow-water distribution 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 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.
This article appeared on pages 4-5 of the 2017 SDRP Annual Report, Nicks n Notches.