The term "Unusual Mortality Event" (UME) refers to a significant die-off of a marine mammal population, where the number of deaths exceeds the expected or normal mortality rate for that species. This phenomenon has become a pressing concern in recent years, with numerous UMEs reported globally, affecting various marine mammal species. The National Oceanic and Atmospheric Administration (NOAA) is responsible for investigating UMEs in the United States, working in collaboration with other federal and state agencies, as well as non-governmental organizations.
Causes of Unusual Mortality Events
UME investigations often reveal a complex interplay of factors contributing to the die-off. Environmental factors, such as extreme weather events, ocean temperature fluctuations, and changes in prey distribution, can play a significant role. For instance, harmful algal blooms have been linked to several UMEs, as these blooms can produce toxins that are harmful to marine mammals. Additionally, human activities, such as entanglement in fishing gear, ship strikes, and noise pollution, can also contribute to UMEs. In some cases, disease outbreaks can be the primary cause of a UME, highlighting the importance of monitoring marine mammal health and detecting potential outbreaks early.
Examples of Unusual Mortality Events
One notable example of a UME is the 2019 die-off of gray whales along the West Coast of North America. During this event, over 200 gray whales were found dead, with many more reported injured or stranded. Investigations suggested that malnutrition was a primary factor, likely due to changes in prey availability and quality. Another example is the 2018 UME affecting bottlenose dolphins in the Gulf of Mexico, where over 150 dolphins were found dead. In this case, toxic algae were suspected to be the cause, as high levels of toxins were detected in the dolphins’ tissues.
| Year | Species | Location | Number of Deaths | Suspected Cause |
|---|---|---|---|---|
| 2019 | Gray Whale | West Coast, North America | 200+ | Malnutrition |
| 2018 | Bottlenose Dolphin | Gulf of Mexico | 150+ | Toxic Algae |
| 2017 | Seal | Alaska | 100+ | Disease Outbreak |
Investigating Unusual Mortality Events
UME investigations involve a comprehensive approach, incorporating field observations, laboratory analysis, and statistical modeling. Field observations involve documenting the location, number, and condition of dead or stranded animals, as well as collecting tissue samples for laboratory analysis. Laboratory analysis includes histopathology, toxicology, and microbiology tests to identify potential causes of death. Statistical modeling helps to identify patterns and trends in the data, informing the development of hypotheses and testing of potential causes.
Challenges in Investigating Unusual Mortality Events
Investigating UMEs can be challenging due to the remote location of many marine mammal populations, making it difficult to access and collect data. Additionally, decomposition of carcasses can occur rapidly, limiting the time available for sampling and analysis. Furthermore, limited funding and resources can constrain the scope and effectiveness of UME investigations, highlighting the need for collaborative efforts and strategic planning.
What is an Unusual Mortality Event (UME)?
+An Unusual Mortality Event (UME) is a significant die-off of a marine mammal population, where the number of deaths exceeds the expected or normal mortality rate for that species.
What are the common causes of UMEs?
+Common causes of UMEs include environmental factors, human activities, and disease outbreaks. Environmental factors such as extreme weather events, ocean temperature fluctuations, and changes in prey distribution can contribute to UMEs. Human activities like entanglement in fishing gear, ship strikes, and noise pollution can also play a role. Disease outbreaks can also be a primary cause of UMEs.
How are UMEs investigated?
+UME investigations involve a comprehensive approach, incorporating field observations, laboratory analysis, and statistical modeling. Field observations document the location, number, and condition of dead or stranded animals, while laboratory analysis includes histopathology, toxicology, and microbiology tests to identify potential causes of death. Statistical modeling helps to identify patterns and trends in the data, informing the development of hypotheses and testing of potential causes.
