2010–2014 Cetacean Unusual Mortality Event in Northern Gulf of Mexico (Closed)

Overview

Under the Marine Mammal Protection Act, an Unusual Mortality Event  was declared for dolphins and whales (cetaceans) in the northern Gulf of Mexico (Texas/Louisiana border through Franklin County, FL) in early 2010.

Based on analysis of stranding data and recommendations from the UME investigative team and the Working Group on Marine Mammal Unusual Mortality Events (an advisory group of marine mammal health and biology experts), NOAA has declared the northern Gulf of Mexico cetacean UME closed. The investigation results of the cetacean UME in the northern Gulf of Mexico are available on our website. Results and publications will continue to be updated as they become available.

The temporal and spatial boundaries have been redefined to include the following:

• All cetaceans stranded in Alabama, Mississippi, and Louisiana from March of 2010–July of 2014, and
• All cetaceans other than bottlenose dolphins stranded in the Florida Panhandle (Franklin County through Escambia County) from March 2010–July of 2014. These boundaries could be adjusted in the future based upon the availability of new results or analyses.

The UME investigation and the Deepwater Horizon Natural Damage Resource Assessment have determined that the Deepwater Horizon oil spill resulted in the death of marine mammals and is the most likely explanation of the persistent, elevated stranding numbers in the northern Gulf of Mexico after the spill.

The evidence to date supports the hypothesis that exposure to Deepwater Horizon petroleum products was the most likely explanation of the adrenal and lung disease in dolphins, which has contributed to increased deaths and fetal loss among dolphins living within the oil spill footprint. While the number of dolphin mortalities in the area decreased after the peak from March 2010–July 2014, it does not indicate that the effects of the oil spill on these populations have ended.

Researchers still saw evidence of chronic lung disease and adrenal impairment even 4 years after spill (in July 2014), and saw evidence of failed pregnancies in 2015. Research into the long-term health effects of the spill on marine mammal populations is ongoing.  For more information on proposed restoration and monitoring activities please see the Final Programmatic Damage Assessment and Restoration Plan (PDARP) for the Gulf of Mexico. Additionally, more details are available on NOAA’s investigation results page.

These numbers are preliminary and may be subject to change. The UME involves 1,141 cetacean strandings in the Northern Gulf of Mexico. Five percent of the cetacean strandings were alive, while 95 percent were stranded dead.

*This number includes 13 dolphins that were killed incidental to fish related scientific data collection and one dolphin killed incidental to trawl relocation for a dredging project.

**The initial response phase ended for all four states on November 2, 2010. Response re-opened for eastern and central Louisiana on December 3, 2010 and closed again on May 25, 2011.

Brucella Infection

In addition to investigating all other potential causes, scientists investigated what role Brucella bacteria had in the UME.

Since our finding of Brucella in 5 stranded dolphins from Louisiana in 2011, scientists tested cases that showed pathological changes consistent with the fetal pneumonia or adult meningitis identified in the first five cases. A total of 68 of 210 dolphins tested positive or equivocal for Brucella. Additional information about Brucella in stranded dolphins can be found in Colegrove et al. 2016.

Learn more about Brucella infection in whales and dolphins

Data for All Stranded Cetaceans

Data for Stranded Bottlenose Dolphins (All Size Classes)

Data for Premature, Stillborn, or Neonatal Bottlenose Dolphins (with less than 115 cm Total Length)

More Information

• Deepwater Horizon oil spill: Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement.
• Investigation Results of the Cetacean Unusual Mortality Event in Northern Gulf of Mexico.
• Marine Mammal Health and Stranding Response Program.
• Marine Mammal Protection.
• Unusual Mortality Events.