Marine Mammal Unusual Mortality Events occurring at record levels
By Randall Wells, PhD, Chair, Working Group on Marine Mammal Unusual Mortality Events

       Following the large-scale mortality of bottlenose dolphins along the U.S. Atlantic seaboard in 1987-1988, and the occurrence of even larger mortality events in European waters involving seals and dolphins, NOAA’s Fisheries Service (NMFS), with involvement by the U.S. Fish and Wildlife Service, established the Working Group on Marine Mammal Unusual Mortality Events (WG) in the early 1990’s.  Figure 2. "FB28" with fungal disease, lobomycosis, on his dorsal fin. Merrily's brand-new third calf swims alongside in July 2005.I was a charter member of the original WG, and after being asked to return to the WG in 2004, I currently serve as chair.  The WG is tasked with determining when a situation involving unusual deaths or illnesses of marine mammals warrants formal designation as an Unusual Mortality Event (UME), which then sets in motion a scientific investigation process and makes federal funds available.
       The following criteria are used to evaluate whether an event qualifies as a UME:
       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.

Figure 1. Numbers of Unusual Mortality Events in the United States, showing dramatic increase in recent years.

       Members of the WG are consulted, and must vote on determination of a UME within 24 hours of submission of an initiation request for consideration.  If a UME is designated, investigation coordinators are identified, investigation plans are reviewed by the WG, and a member of the WG becomes a liaison/mentor for that specific investigation.  The number of open investigations has increased dramatically over the past three years, from five in 2005, to a record 13 events being investigated in 2007.  Current UMEs cover the spectrum of marine mammals, from manatees and bottlenose dolphins in the Gulf of Mexico, to sea otters in Alaska and blue whales off California.  Hypothesized causes for these UMEs are varied, but harmful algal blooms are associated with a number of them.

Figure 3. Bottlenose dolphin "Val" with skin lesions, undergoing rehabilitation at Mote Marine Laboratory during Florida West Coast Multi-Species UME. "Val" was subsequently released and monitored for about one month.