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2011-2012 Bottlenose Dolphin Unusual Mortality Event in Texas


Bottlenose Dolphin with calf
Bottlenose Dolphins
(Tursiops truncatus)
Photo: NMFS Southwest
Fisheries Science Center

On May 9, 2012, NOAA declared an Unusual Mortality Event (UME) for bottlenose dolphins in Texas. The UME lasted from November 2011-March 2012 and included 126 bottlenose dolphins. The majority of those stranded in 5 counties: Aransas, Calhoun, Kleburg, Galveston, and Brazoria.

Under the Marine Mammal Protection Act, a UME is defined as a stranding event that is unexpected, involves a significant die-off of any marine mammal population, and demands immediate response.

There are 7 criteria used to determine whether a mortality event is "unusual." A group of marine mammal experts, called the Working Group on Marine Mammal Unusual Mortality Events, determines whether strandings meet one or more of the criteria before officially declaring an Unusual Mortality Event. The experts concluded that that dolphin strandings in Texas met at least 3 of the 7 criteria established for designation of an Unusual Mortality Event. They were:

  • A marked increase in the magnitude or a marked change in the nature of morbidity, mortality, or strandings when compared with prior records.
  • The species, age, or sex composition of the affected animals is different than that of animals that are normally affected.
  • Affected animals exhibit similar or unusual pathologic findings, behavior patterns, clinical signs, or general physical condition (e.g., blubber thickness).

The following questions and answers address the details related to this UME declaration. More information on all recent UMEs is available on our website.

Q: When did the first reports of increased strandings of dolphins come in?

A: In November 2011, the Texas Marine Mammal Stranding Network started to notice an increase in bottlenose dolphin strandings in the region. The increase, especially of young dolphins less than one year old, continued through February 2012.

Q: Do we know why these animals stranded?

A: No, we do not know why these animals stranded. Of the 123 animals stranded, only 4 were found alive. Preliminary findings included:

  • infection in the lung
  • poor body condition
  • discoloration of the teeth
  • in four animals, a black/grey, thick mud-like substance in the stomachs was found

The strandings were coincident with a harmful algal bloom of Karenia brevis that started in September 2011 in southern Texas, but researchers have not determined that was the cause of the event. Currently, there are no red tide blooms occurring in the region, and stranding rates have returned to normal levels.

map of bottlenose strandings in Texas
Tursiops strandings: Nov 2011-Mar 2012
Credit: NOAA

Q: Have other marine mammals been affected by this die-off event?

A : No, but there have been numerous fish kills and bird die-offs in the same geographic area.

Q: What are the next steps in the investigation now that an Unusual Mortality Event was declared?

A: As part of the Unusual Mortality Event investigation process, an independent team of scientists (investigation team) is being assembled to coordinate with the Working Group to review the data collected and to determine potential next steps. These investigations may require months, or even years, of data collection and analysis.

Q: What additional resources are now available to pursue the investigation, since an Unusual Mortality Event has been declared?

A: An Unusual Mortality Event declaration provides additional expertise from the Working Group (an international and multi-disciplinary team of scientists), additional partners, and access to additional funding through the National Contingency Fund.

In addition, this will provide a detailed investigative plan for the investigation. This may include

  • more targeted necropsies
  • further testing of samples for biotoxins, bacterial or viral agents
  • diagnostic pathology services

Finally, this will provide national and international scientific review of findings and interpretations.

Q: Will you be collecting additional biological and environmental information?

A: The Stranding Network will continue to collect and analyze samples as needed to evaluate the situation. The decision on whether additional information is needed will be made by the Unusual Mortality Event Working Group.

Q: When will you have some results to share?

A: The investigative team is taking the results from pathology and epidemiology studies to guide the direction of additional analyses into factors that may be contributing to or causing mortalities in the bottlenose dolphins.

To date, about 36 full necropsies have been completed on fresh to moderate dolphin carcasses by several teams of pathologists and veterinarians. Blood and tissue samples from dead animals will be tested for bacterial and biotoxin agents, which may be responsible for the animals' condition.

It typically takes months to years to complete an investigation, and many times we are unable to determine the cause of the event.

Q: What is the risk to humans?

A: It is not clear if there is any risk to human health through contact. To date, no cases of human illness have been reported from this current event. However, because marine mammals and people can share diseases, you should stay away from marine mammals (either live or dead marine mammals) that are stranded on the beach. Pets should also be kept away from diseased or dead marine mammals.

Q: How many marine mammal Unusual Mortality Events have previously occurred in Texas?

A: This is the fifth (5) marine mammal Unusual Mortality Event to have occurred in Texas. Unusual Mortality Events were declared in Texas in 1992, 1994, 2007, and 2008.

All previous events involved bottlenose dolphins.

For the 1994 event, morbillivirus infection was determined to be the cause of the mortality; the cause is still undetermined for the other 3 events.

Q: How many marine Unusual Mortality Events have previously occurred in the Gulf of Mexico?

A: This is the nineteenth (19) marine mammal Unusual Mortality Event to have occurred in the Gulf of Mexico. All previous events involved either bottlenose dolphins, other species of cetaceans (whales and dolphins), and/or manatees.

To date, 60 total Unusual Mortality Events have been formally declared in U.S. waters since 1991 (including the current Unusual Mortality Event).

Q: How does the Unusual Mortality Event in Texas relate to the declared Unusual Mortality Event in the Northern Gulf of Mexico involving dolphins?

A: At this time, there is no obvious relationship between these two events. However, our pathologists are comparing samples to see if a relationship does exist and more will be known once the samples have been analyzed. For more information on the declared Unusual Mortality Event in the Northern Gulf of Mexico involving dolphins.

Q: Where can I find additional information on bottlenose dolphins and other Unusual Mortality Events?

A: You can visit the national NOAA Fisheries Protected Resources' websites on bottlenose dolphins and Unusual Mortality Events.

Q: What should people do if they encounter a dolphin on the beach?

A: Dolphins live only in the water and should not be found on the beach. Any live dolphin on a beach is an emergency situation. Please contact your local stranding network or local authorities to report a live or dead stranded dolphin.

  • Do not allow pets to approach the dolphin;
  • Do not attempt to push a live animal back out to sea;
  • Report sick or dead marine mammals to the Southeast Marine Mammal Stranding Hotline:
    • 1-877-WHALE-HELP (1-877-942-5343)

Q: What should people do if they witness harassment of a dolphin in the water?

A: To report violations or for more information on NOAA's Office of Law Enforcement:

  • 1-800-853-1964

Updated: March 10, 2014

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