Demographic clusters identified within the northern Gulf of Mexico common bottlenose dolphin (Tursiops truncates) unusual mortality event: January 2010-June 2013.

A multi-year unusual mortality event (UME) involving primarily common bottlenose dolphins (Tursiops truncates) was declared in the northern Gulf of Mexico (GoM) with an initial start date of February 2010 and remains ongoing as of August 2014. To examine potential changing characteristics of the UME over time, we compared the number and demographics of dolphin strandings from January 2010 through June 2013 across the entire GoM as well as against baseline (1990-2009) GoM stranding patterns. Years 2010 and 2011 had the highest annual number of stranded dolphins since Louisiana's record began, and 2011 was one of the years with the highest strandings for both Mississippi and Alabama. Statewide, annual numbers of stranded dolphins were not elevated for GoM coasts of Florida or Texas during the UME period. Demographic, spatial, and temporal clusters identified within this UME included increased strandings in northern coastal Louisiana and Mississippi (March-May 2010); Barataria Bay, Louisiana (August 2010-December 2011); Mississippi and Alabama (2011, including a high prevalence and number of stranded perinates); and multiple GoM states during early 2013. While the causes of the GoM UME have not been determined, the location and magnitude of dolphin strandings during and the year following the 2010 Deepwater Horizon oil spill, including the Barataria Bay cluster from August 2010 to December 2011, overlap in time and space with locations that received heavy and prolonged oiling. There are, however, multiple known causes of previous GoM dolphin UMEs, including brevetoxicosis and dolphin morbillivirus. Additionally, increased dolphin strandings occurred in northern Louisiana and Mississippi before the Deepwater Horizon oil spill. Identification of spatial, temporal, and demographic clusters within the UME suggest that this mortality event may involve different contributing factors varying by location, time, and bottlenose dolphin populations that will be better discerned by incorporating diagnostic information, including histopathology

Magnitude of numbers of stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) above the upper baseline limit (1990–2009) in the northern Gulf of Mexico during the ongoing unusual mortality event (January 2010-June 2013).

<p>From west to east; A) Texas, B) Western Louisiana C) Barataria Bay, Louisiana, D) Northern Louisiana, E) Mississippi, and F) Alabama, G) Florida Panhandle, and H) Western Florida. The solid box marked ‘Pre-spill’ represents time before the <i>Deepwater Horizon</i> oil spill in the northern Gulf of Mexico.</p

Comparison of demographics for common bottlenose dolphins (<i>Tursiops truncatus</i>) stranded in Mississippi and Alabama during shared large-scale mortality years (LSMY) 1990 and 2011.

<p>Louisiana 2011 was compared to Mississippi and Alabama 2011 due to Louisiana’s relative longevity of high stranding rates. The ongoing dolphin Gulf of Mexico (GoM) unusual mortality event (UME) includes years 2010 and 2011.</p><p>Comparison of demographics for common bottlenose dolphins (<i>Tursiops truncatus</i>) stranded in Mississippi and Alabama during shared large-scale mortality years (LSMY) 1990 and 2011.</p

Baseline historical stranding numbers of common bottlenose dolphins (<i>Tursiops truncatus</i>) in the northern Gulf of Mexico, fitted values, and the upper 95% confidence limit from negative-binomial regression model for regions with statewide annual increases during the ongoing northern Gulf of Mexico unusual mortality event; A) Texas, B) Western Louisiana, C) Barataria Bay, Louisiana D) Northern Louisiana, E) Mississippi, F) Alabama, G) Florida Panhandle, H) Western Florida.

<p>Baseline historical stranding numbers of common bottlenose dolphins (<i>Tursiops truncatus</i>) in the northern Gulf of Mexico, fitted values, and the upper 95% confidence limit from negative-binomial regression model for regions with statewide annual increases during the ongoing northern Gulf of Mexico unusual mortality event; A) Texas, B) Western Louisiana, C) Barataria Bay, Louisiana D) Northern Louisiana, E) Mississippi, F) Alabama, G) Florida Panhandle, H) Western Florida.</p

Map of the U.S. Gulf Coast showing county groups used in analysis of regional monthly baseline common bottlenose dolphin (<i>Tursiops truncatus</i>) stranding numbers.

<p>Baselines for Texas and Western Florida were determined by combining multiple regions outlined below. Gulf Florida includes the Florida Panhandle and the Western Florida combined region.</p

Hematoxalin and eosin (HE) stained section of lung from an adult female common bottlenose dolphin (<i>Tursiops truncatus</i>) that stranded in Barataria Bay, Louisiana in December 2011 with primary bacterial pneumonia.

<p>Airspaces and septae are obscured by accumulations of neutrophils and fibrous connective tissue that surround large bacterial colonies (arrows). Bar = 500 μm.</p

Adrenal Gland and Lung Lesions in Gulf of Mexico Common Bottlenose Dolphins (<i>Tursiops truncatus</i>) Found Dead following the <i>Deepwater Horizon</i> Oil Spill

<div><p>A northern Gulf of Mexico (GoM) cetacean unusual mortality event (UME) involving primarily bottlenose dolphins (<i>Tursiops truncatus</i>) in Louisiana, Mississippi, and Alabama began in February 2010 and continued into 2014. Overlapping in time and space with this UME was the <i>Deepwater Horizon</i> (DWH) oil spill, which was proposed as a contributing cause of adrenal disease, lung disease, and poor health in live dolphins examined during 2011 in Barataria Bay, Louisiana. To assess potential contributing factors and causes of deaths for stranded UME dolphins from June 2010 through December 2012, lung and adrenal gland tissues were histologically evaluated from 46 fresh dead non-perinatal carcasses that stranded in Louisiana (including 22 from Barataria Bay), Mississippi, and Alabama. UME dolphins were tested for evidence of biotoxicosis, morbillivirus infection, and brucellosis. Results were compared to up to 106 fresh dead stranded dolphins from outside the UME area or prior to the DWH spill. UME dolphins were more likely to have primary bacterial pneumonia (22% compared to 2% in non-UME dolphins, <i>P</i> = .003) and thin adrenal cortices (33% compared to 7% in non-UME dolphins, <i>P</i> = .003). In 70% of UME dolphins with primary bacterial pneumonia, the condition either caused or contributed significantly to death. Brucellosis and morbillivirus infections were detected in 7% and 11% of UME dolphins, respectively, and biotoxin levels were low or below the detection limit, indicating that these were not primary causes of the current UME. The rare, life-threatening, and chronic adrenal gland and lung diseases identified in stranded UME dolphins are consistent with exposure to petroleum compounds as seen in other mammals. Exposure of dolphins to elevated petroleum compounds present in coastal GoM waters during and after the DWH oil spill is proposed as a cause of adrenal and lung disease and as a contributor to increased dolphin deaths.</p></div

Prevalence comparisons of causes of death for fresh dead, stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) among 1) unusual mortality event cases from Louisiana, Mississippi, and Alabama, 2) slide-reviewed and standardly scored reference dolphin subset, 3) Barataria Bay, Louisiana UME dolphin subset, and 4) all reference dolphins.

<p>Denominators varied based upon information available, tissues collected from, and tests conducted on individual UME and reference dolphins.</p><p>*Values different (<i>P</i> < 0.05) than reference dolphins.</p><p>Prevalence comparisons of causes of death for fresh dead, stranded common bottlenose dolphins (<i>Tursiops truncatus</i>) among 1) unusual mortality event cases from Louisiana, Mississippi, and Alabama, 2) slide-reviewed and standardly scored reference dolphin subset, 3) Barataria Bay, Louisiana UME dolphin subset, and 4) all reference dolphins.</p