Slow recovery of Barataria Bay dolphin health following the Deepwater Horizon oil spill (2013-2014), with evidence of persistent lung disease and impaired stress response

Abstract

The 2010 Deepwater Horizon (DWH) disaster resulted in large-scale oil contamination of the northern Gulf of Mexico. As part of the Natural Resource Damage Assessment designed to investigate the potential impacts of the DWH oil spill, comprehensive health assessments were conducted on bottlenose dolphins Tursiops truncatus living in oiled bays (Barataria Bay [BB], Louisiana, and Mississippi Sound [MS], Mississippi/Alabama) and a reference bay with no evidence of DWH oil contamination (Sarasota Bay [SB], Florida). As previously reported, multiple health issues were detected in BB dolphins during 2011. In the present study, follow-on capturerelease health assessments of BB dolphins were performed (2013, 2014) and indicated an overall improvement in population health, but demonstrated that pulmonary abnormalities and impaired stress response persisted for at least 4 yr after the DWH disaster. Specifically, moderate to severe lung disease remained elevated, and BB dolphins continued to release low levels of cortisol in the face of capture stress. The proportion of guarded or worse prognoses in BB improved over time, but 4 yr post-spill, they were still above the proportion seen in SB. Health assessments performed in MS in 2013 showed similar findings to BB, characterized by an elevated prevalence of low serum cortisol and moderate to severe lung disease. Prognosis scores for dolphins examined in MS in 2013 were similar to BB in 2013. Data from these follow-on studies confirmed that dolphins living in areas affected by the DWH spill were more likely to be ill; however, some improvement in population health has occurred over time.

Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill

“…7c). Our low survival estimates for this period, concurrent high stranding rates, and general poor health of Barataria Bay dolphins documented during separate health assessments (Lane et al 2015, Smith et al 2017, this Theme Section) strongly support the notion that increased mortality occurred during this period.…”

Low reproductive success rates of common bottlenose dolphins Tursiops truncatus in the northern Gulf of Mexico following the Deepwater Horizon disaster (2010-2015)

“…The primary health effects documented in oiled dolphin stocks during and after the DWH oil spill include high rates of atypical pulmonary and adrenal diseases and disproportionate rates of poor body condition (Schwa cke et al 2014, Smith et al 2017. Un treated pulmonary disease can cause complications during human pregnancy and early development, leading to greater likelihood of fetal and neo natal mortality (Ramsey & Ramin 2001, Ie et al 2002, Hartert et al 2003, Goodnight & Soper 2005.…”

“…Poor maternal lung function limits the ability to provide the additional oxygen needed leading to greater likelihood of early terminations, poor fetal development, or spontaneous abortions (Goodnight & Soper 2005). Another major health effect ob served in the DWH oiled areas was impaired adrenal corticosteroid hormone production or hypoadrenocorticism (Schwacke et al 2014, Smith et al 2017. Humans with im paired adrenal cortex function have a higher risk of adrenal crisis, which is linked to higher fetal and maternal mortality when left untreated (Brent 1950, KellerWood & Wood 2001, Ambrosi et al 2003, Beehner et al 2006.…”

“…Moreover, mortality rates in heavily-oiled Barataria Bay, LA, and Mississippi Sound, MS, were approximately 2.5 to 3.5 times higher than those of non-oiled areas, as estimated from the boatbased follow-up surveys of animals examined during capture-release health assessments (CRHA) (Lane et al 2015, Deepwater Horizon Natural Resource Damage Assessment Trustees 2016). The CRHAs of the Barataria Bay and Mississippi Bay animals also revealed a disproportionate number of grossly underweight individuals (Schwacke et al 2014) and a high prevalence of lung disease and evidence of adrenal insufficiency that continued until at least 2014 (Schwacke et al 2014, Smith et al 2017, this Theme Section). The results from these live animals are consistent with histological studies of dolphins stranded after the spill in the oiled waters of Louisiana, Mississippi, and Alabama, which found significantly higher rates of bacterial pneumonia and abnormally thin adrenal cortices relative to animals outside the region or with individuals collected before the spill (Venn-Watson et al 2015a).…”

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

“…The official ending of the UME on 31 July 2014, and follow-up assessments of live dolphins 3 and 4 yr post-spill suggest that the health of nearshore dolphins has improved , this Theme Section). However, the prevalence of moderate to severe lung disease and impaired stress response continues to be higher than expected (as of summer 2014; see Smith et al 2017), indicating there are lingering health effects for the dolphin cohorts exposed to DWH oil that will likely continue to affect survival. Likewise, the rate of reproductive failure remained elevated through spring 2015 when the final Natural Resource Damage Assessment (NRDA) bottlenose dolphin surveys were conducted (Kellar et al 2017).…”