Project Overview

Summary:

In January 2016, Dr. Cynthia Smith at the National Marine Mammal Foundation was awarded an RFP-V grant of $2,460,921 to lead the GoMRI project entitled Investigation of Mechanisms for Reproductive Failure in the Aftermath of the Deepwater Horizon Oil Spill to Understand Population Recovery Scenarios for Cetaceans which consisted of 4 collaborative institutions and approximately 38 research team members (including students). The overall goal of this project was to investigate direct and indirect factors involved in the reproductive impairment observed in bottlenose dolphins following the Deepwater Horizon(DWH) oil spill in order to better understand the process for population recovery.  It developed and tested cutting-edge medical technologies for evaluating potential reproductive system disorders and then integrated those technologies into dolphin capture-release field studies in Barataria Bay, Louisiana.  This project included both retrospective (banked samples from successful and failed pregnancies) and prospective sampling of dolphins 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. The paired studies using the Barataria Bay and Navy dolphin populations not only provided a mechanism to refine and validate innovative diagnostic techniques for marine mammals, but also provided valuable insight into the progression and potential mechanisms of disease that increase the risk of a negative reproductive outcome.

Research Highlights

            As of June 30, 2019, this project’s research, which entailed around 5 research expeditions and 32 photo-ID field studies, resulted in 5 peer-reviewed publications, 8 scientific presentations, and 17 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which have all been made available to the public. Since then, an additional 2 peer-reviewed articles have been published, 1 accepted, 1 submitted, and 3 are in preparation; therefore, we expect at least 10 publications to be attributed to this grant.  Five more datasets are expected to be submitted to GRIIDC following final review by the US Navy’s public affairs office.  The project also engaged 2 Masters and Ph.D. students over its award period, and 2 Veterinary Post-Doctoral Fellows. The research was highlighted in the documentary films, Dispatches from the Gulf 2 and Dispatches from the Gulf 3. Significant outcomes of this project’s research according to GoMRI Research Theme 3 are highlighted below.

(1)   Dolphins living within the oil spill footprint have a sustained high reproductive failure rate. Through our capture-release health assessments which focused on fetal, placental, and maternal health of Barataria Bay dolphins, and our photo-ID field studies focused on reproductive outcomes, we documented a continuation of the low reproductive success rate of only 20% within the oil spill footprint. The success rate has remained fairly consistent at ~20% for all years surveyed since the DWH spill (health and reproductive assessments performed in 2011, 2013, 2014, 2016, 2017, and 2018; 44 dolphin pregnancies diagnosed and monitored during that time period).  It should be noted that 16% of the outcomes remain unknown due to the disappearance and likely death of some of those pregnant dolphins. However, even if all of the missing females were successful, this would only be a reproductive success rate of 36%, which is still much lower than the combined success rate of bottlenose dolphins living outside the oil spill footprint (67%).  

(2)   Chronic maternal illness in the aftermath of the DWH oil spill is the likely cause of reproductive failure.  Normal ultrasound progression of fetal development in utero and retrospective examination of pregnancies with known failed outcome has enabled several hypotheses as to the potential mechanisms of pregnancy failure, with maternal illness standing out unequivocally as the most important predictor for pregnancy complications. To inform this assessment, ~300 fetal and placental ultrasound exams of dolphins in human care were assessed retrospectively, including parameters such as fetal biparietal diameter (BPD), thoracic width in dorsal and transverse planes, thoracic height in a sagittal plane, aortic diameter, blubber thickness, fetal lung:liver echogenicity, fetal movement, uteroplacental thickness and separation, change in corpus luteum size, and umbilical cord abnormalities. These data were integrated with the complete veterinary case history for each dam and the resulting fetal and placental histopathology findings to elucidate maternal, placental, and fetal predictors of pregnancy failure. This thorough and exhaustive analysis has proven pivotal for our understanding of reproductive failure in dolphins and has provided a mechanistic model with which to analyze and interpret wild dolphin cases, even if only a single exam is available.

In light of these analyses, potential mechanisms of failure in managed dolphins included maternal illness, placental dysfunction, and less commonly in utero infections and congenital defects. A majority of managed dolphin pregnancy failures (59%) commenced with maternal illness and 32% with placental dysfunction. Using the newly established predictors of pregnancy loss, this pattern also proved consistent in our wild dolphin cases with 96% of the pregnancy failures in Barataria Bay showing signs of maternal illness and 65% showing placental dysfunction. The enhancement of our health assessment methods has allowed us to confirm that poor maternal illness was the most likely initial cause of failure, with supporting evidence of placental dysfunction on reproductive ultrasound exams, as early as the 1st trimester of pregnancy. Additionally, maternal oxygenation data showed that pulmonary disease, already documented in Barataria Bay dolphins, is likely contributing to acid-base imbalances. The continued prevalence of pulmonary disease could also be causing low-grade, sustained fetal hypoxia in addition to maternal illness, exacerbating fetal distress.

Ongoing health assessments have included pulmonary evaluations, which have informed the analysis. The prevalence of moderate to severe lung disease in Barataria Bay dolphins, when compared to dolphins outside the oil spill footprint, remains elevated. Lungs were scored as moderate to severe in 30% of dolphins in 2017 and 45% in 2018, significantly higher than the 7% in reference site dolphins (Sarasota Bay). Additionally, moderate to severe alveolar interstitial syndrome (AIS) remained a common finding in Barataria Bay dolphins, with a significantly higher prevalence in all years when compared to Sarasota Bay dolphins. The distribution of AIS in Barataria Bay dolphins has shifted to a worsening dorsal to ventral pattern. This could be consistent with pulmonary edema, chronic progressive pulmonary fibrosis, or another pulmonary pathology. Overall, the prevalence of pulmonary disease is contributing to the overall poor maternal health of Barataria Bay dolphins, which in turn is contributing to the sustained high reproductive failure rate.

Based on the medical data generated by this study, we do not expect the maternal reproductive failure rate to improve until the overall health of reproductive females in Barataria Bay improves. With the sustained low reproductive success rate in Barataria Bay, it is essential that maternal health is continuously monitored and addressed.

(3)   Enhanced health assessment methods developed during this research project represent a significant advancement in dolphin medicine, conservation medicine, and veterinary medicine.  The techniques and tools developed have greatly enhanced our ability to diagnose fetal and placental disease in marine mammals and enabled the prediction of reproductive outcomes with blood-based, exhaled gases, and diagnostic ultrasound methods. Additional techniques were also developed to advance our overall approach to health assessments of wild cetaceans. The following are examples of the medical and scientific contributions made by our team under this GoMRI-funded study.

• Similar to the fetal and placental ultrasound examinations performed on human fetuses, we have developed a comprehensive technique to evaluate dolphin pregnancies and determine fetal well-being and placental health. The novel technique allows for the rapid and accurate diagnosis of stage of pregnancy, indication of fetal and placental health, and prediction of reproductive outcome. The resulting manuscript, entitled “Ultrasonographic findings associated with normal pregnancy and fetal well-being in the bottlenose dolphin (Tursiops truncatus),” has been accepted for publication by Veterinary Radiology and Ultrasound. Illustrations of fetomaternal anatomical structures by trimester were created, allowing for the first ever visual reference of dolphin fetomaternal anatomy as it correlates to ultrasound examination. We expect this to become a landmark paper in the field of cetacean medicine, with the potential to generate positive impacts on reproductive efforts of protected and endangered cetacean species, predict reproductive outcomes and inform medical intervention strategies, and allow for the rapid diagnosis of pathologic mechanisms that could lead to failure.
  
  
• Based on the robust data generated from Navy dolphin pregnancies, we have also established normal exhaled gases and blood-based values (including complete blood counts, blood chemistry, hormones, and blood gases) in both successful and failed pregnancies, allowing for the detection of pregnancy abnormalities and providing indicators of pregnancy failure.  The publication of these data is in process, beginning with a recent publication in Theriogenology entitled, “Pregnancy profiles in the common bottlenose dolphin (Tursiops truncatus): Clinical biochemical and hematological variations during healthy gestation and a successful outcome.”
  
  
• We have facilitated the completion of an innovative method for aging wild dolphins that will likely eliminate tooth extraction for aging purposes in field protocols, which represents a major advancement in cetacean conservation medicine. The resulting manuscript is entitled “Radiographic assessment of pectoral flippers in common bottlenose dolphins to estimate chronological age” and was recently published by PLOS One. 

 Proposal Abstract - RFP-V PI Cynthia R. Smith