Understanding Marine Mammal Unusual Mortality Events

An unusual mortality event, or UME for short, is defined under the Marine Mammal Protection Act as a stranding event that is unexpected, involves a significant die-off of any marine mammal population, and demands immediate response. There are seven criteria that make a mortality event "unusual." If the national Working Group on Marine Mammal Unusual Mortality Events, a group of marine mammal health experts, determines that an event meets one or more of the criteria, then it forwards a recommendation to NOAA’s Assistant Administrator for Fisheries to declare a UME.

The Working Group on Marine Mammal Unusual Mortality Events developed a set of criteria for determining an unusual mortality event:

1. A marked increase in the magnitude or a marked change in the nature of morbidity, mortality, or strandings when compared with prior records.
2. A temporal change in morbidity, mortality, or strandings is occurring.
3. A spatial change in morbidity, mortality, or strandings is occurring.
4. The species, age, or sex composition of the affected animals is different than that of animals that are normally affected.
5. Affected animals exhibit similar or unusual pathologic findings, behavior patterns, clinical signs, or general physical condition (e.g., blubber thickness).
6. Potentially significant morbidity, mortality, or stranding is observed in species, stocks, or populations that are particularly vulnerable (e.g., listed as depleted, threatened, or endangered or declining). For example, stranding of three or four right whales may be cause for great concern whereas stranding of a similar number of fin whales may not.
7. Morbidity is observed concurrent with or as part of an unexplained continual decline of a marine mammal population, stock, or species.

Any of these criteria may indicate an unusual mortality event.

For more information, see the Federal Register notice (71 FR 75234), published on December 14, 2006, that announced these criteria.

It authorizes a federal investigation led by the expertise of the working group to the investigate the event and focus:

• To minimize deaths.
• To determine the event cause.
• To determine the effect of the event on the population.
• To identify the role of environmental parameters in the event.

We have a list of all active and closed UMEs on our website. 

UMEs have occurred in coastal waters throughout the United States. The states with the highest number of declared UMEs are California and Florida.

Bottlenose dolphins, California sea lions, and manatees are the most common marine mammals involved in UMEs.

While the cause of many UMEs is unknown, the investigation aims to determine the cause of all UMEs, when possible. These causes have included infections, biotoxins, human interactions and malnutrition.

Brevetoxin and domoic acid are the most common biotoxins associated with UMEs, primarily in bottlenose dolphins, manatees, and California sea lions.

In 1991, NOAA Fisheries established the working group in response to large numbers of marine mammal mortalities in the late 1980s. The working group was formalized when Congress passed the 1992 amendments to the Marine Mammal Protection Act (MMPA) as the Marine Mammal Health and Stranding Response Act. The working group's primary role is to determine when an unusual mortality event is occurring and to help direct the response and investigation. Investigation of these events has led to a greater understanding of the impacts of human-related and natural causes of mortality in marine mammal populations.

For each UME, the Working Group on Marine Mammal Unusual Mortality Events works with an Investigative Team to try to determine the cause of the UME. Investigative Teams typically include members of the marine mammal stranding network, staff at scientific and academic institutions, as well as government biologists and veterinarians. An UME investigation remains open until the Investigative Team determines that the criteria under which the UME was declared have resolved or have become persistent. They present their findings to the Working Group, who review the data and vote on whether they agree with the closure recommendation. That recommendation is then passed onwards to NOAA Fisheries or the U.S. Fish and Wildlife Service, who will review the recommendation and make the final decision on whether to close the UME.

MMPA section 405 (16 USC 1421d) establishes the Marine Mammal Unusual Mortality Event Fund, describing its purposes and how the public can donate to the fund. According to the MMPA, the fund “shall be available only for use by the Secretary of Commerce, in consultation with the Secretary of the Interior:

• To compensate persons for special costs incurred in acting in accordance with the contingency plan issued under section 1421c(b) of this title or under the direction of an Onsite Coordinator for an unusual mortality event.
• For reimbursing any stranding network participant for costs incurred in preparing and transporting tissues collected with respect to an unusual mortality event for the Tissue Bank.
• For care and maintenance of marine mammal seized under section 1374(c)(2)(D) of this title.”

The National Contingency Plan for Response to Unusual Marine Mammal Mortality Events outlines the types of expenses that are reimbursable under the fund and the process for requesting reimbursement.

Learn more about the UME Contingency Fund

The following can be deposited into the fund:

• Amounts appropriated to the fund.
• Other amounts appropriated to the Secretary for use with respect to UMEs.
• Amounts received by the United States in the form of gifts, devises, and bequests under subsection (d) of section 405(d) of the MMPA.

The public may use Pay.gov to donate to the UME Contingency Fund for this or other UMEs and help cover costs incurred by the Marine Mammal Stranding Network.