False Killer Whale
False Killer Whale
Pseudorca crassidens
Protected Status
ESA Endangered
Main Hawaiian Islands Insular DPS
CITES Appendix II
Throughout Its Range
MMPA Protected
Throughout Its Range
MMPA Depleted
Main Hawaiian Islands Insular stock
Quick Facts
Weight
Up to around 3,000 pounds
Lifespan
Up to 63 years (females); Up to 58 years (males)
Length
Up to 16 feet (females); Up to 20 feet (males)
Threats
Fishery interactions,
Competition with fisheries,
Environmental contaminants,
Hunting (outside United States)
Region
Alaska,
Pacific Islands,
Southeast,
West Coast
About The Species
False killer whales are social animals found globally in all tropical and subtropical oceans and generally in deep offshore waters. The false killer whale’s entire body is black or dark gray, although lighter areas may occur ventrally (on its underside) between the flippers or on the sides of the head.
Fishery interactions is one of the main threats facing this species. False killer whales are known to depredate (take fish and bait off of fishing lines), which can lead to hooking and/or entanglement. This is especially a concern for false killer whales that interact with the Hawaiʻi longline fishery.
Due to its very small population size (about 150 individuals) and population decline in recent decades, the main Hawaiian Islands insular false killer whale distinct population segment (DPS) is listed as endangered under the Endangered Species Act. It is the only false killer whale population protected under the ESA. This stock is also listed as depleted under the Marine Mammal Protection Act.
NOAA Fisheries is committed to conserving and protecting false killer whales. Our scientists and partners use a variety of innovative techniques to study and protect this species.
Status
The broad pelagic distribution of most false killer whale populations make it difficult to estimate the global population size of this species.
The endangered main Hawaiian Islands insular false killer whale is estimated to number around 150 whales. The historical population size is unknown, though spotter planes in the late 1980s observed large aggregations of 350 to 400 whales in a single area. Aerial survey sightings since then suggest that the main Hawaiian Islands insular false killer whale population declined at an average rate of 9 percent per year through at least the early 2000s. The current population trend is unknown.
The cause of this decline is unknown, but it’s thought to be partially due to interactions with fisheries, especially before 1990 when longline fishing was more common in Hawaiʻi’s nearshore waters. Annual variability in survey efforts within the range of the main Hawaiian Islands insular false killer whale make it difficult to assess population trends, so it’s unknown whether the population has continued to decline, recently stabilized, or recently increased.
A survey conducted in 2010 estimated the Hawaiʻi pelagic population of false killer whales to be roughly 1,550 individuals. Their historical population size is also unknown, though interactions with longline fisheries are known to have killed or seriously injured animals in this population since at least the late 1990s. There have been few large-scale surveys in Hawaiian waters, and changes in survey design (intended to provide more precise estimates given the social structure and behavior of false killer whales) make it difficult to determine trends in abundance for this pelagic population.
The Northwestern Hawaiian Islands, northern Gulf of Mexico, and western North Atlantic stocks (populations) are not as well-studied. Current population abundance estimates for all stocks (Hawaiian, the northern Gulf of Mexico, and the western North Atlantic) can be found in the latest marine mammal stock assessment reports.
Learn more about the three populations of false killer whales in Hawaiʻi
Protected Status
ESA Endangered
- Main Hawaiian Islands Insular DPS
CITES Appendix II
- Throughout Its Range
MMPA Protected
- Throughout Its Range
MMPA Depleted
- Main Hawaiian Islands Insular stock
Appearance
False killer whales are large members of the dolphin family. They are dark gray, often appearing black on all but a small part of their ventral (underside) surface, which is lighter between the pectoral fins running from the throat down to the belly.
The species is large and slender, and males are slightly larger than females. They have a small conical head without a beak. The front of an adult male’s head hangs over the lower jaw to a greater extent than in females and is flattened in older males.
The pectoral fins or flippers have a distinct central hump creating an S-shape along the outer edge. The dorsal fin is located in the middle of the back and generally curves backward. In Hawaiian waters, dorsal fin shapes show a lot of variability, often caused by injury from fishery interactions.
Adult females reach lengths of 16 feet, while adult males are almost 20 feet long. In adulthood, large false killer whales can weigh up to 3,000 pounds.
Scientists can photo-identify individual whales through unique natural markings, such as scars to false killer whales’ dorsal fins or scars from cookie cutter sharks. These prominent markings to the body and dorsal fin help distinguish one whale from another.
Behavior and Diet
False killer whales are gregarious and form strong social bonds. They are often found in relatively small subgroups of a single to a few individuals that are associated with a larger aggregation that may spread over tens of kilometers. These strong social bonds between groups and dispersion into small subgroups likely help them find prey.
When they capture prey, many individuals tend to converge, and their prey items may be shared among several animals in the group. In Hawaiʻi, these larger aggregations may include 40 to 50 animals altogether, whereas larger groups have been observed in other regions. They are known to strand in groups as well. In some regions, false killer whales are also found with other cetaceans (whales and dolphins), most notably bottlenose dolphins.
Although the range of the main Hawaiian Islands insular false killer whale partially overlaps with the ranges of the Hawaiʻi pelagic and Northwestern Hawaiian Islands populations, genetic analyses, photo-identification, and social network analyses indicate that the main Hawaiian Islands insular false killer whale population consists of a tight social network that is socially unconnected with the other two Hawaiʻi-based populations.
In addition to the social structure found among all three Hawaiian false killer whale populations, there is significant social structure within the main Hawaiian Islands insular population. A social network analysis indicates that this population can be broadly divided into four primary social clusters.
False killer whales are top predators that primarily hunt fish and squid. They feed both during the day and at night, hunt in dispersed subgroups, and converge when prey is captured. Prey sharing has also been observed among individuals in the group.
False killer whales can dive for up to 18 minutes and swim at high speeds to capture prey at depths of 300 to 500 meters. They often leap completely out of the water, particularly when attacking certain prey species. In Hawaiʻi, they are also known to throw fish high into the air before consuming them.
Where They Live
Habitat
False killer whales generally prefer offshore tropical to subtropical waters that are deeper than 3,300 feet.
Both main Hawaiian Islands insular false killer whales and Northwestern Hawaiian Islands false killer whales maintain a more island-associated habitat, preferring to remain close to the Hawaiian Islands. This is likely due to the islands’ unique oceanographic setting, which concentrates and aggregates prey.
Distribution
False killer whales occur in tropical, subtropical, and temperate waters of all ocean basins. In the United States, they are found around Hawaiʻi, in all Pacific Remote Island Areas, the Mariana Archipelago, and in American Samoa, as well in the Gulf of Mexico and in the warm Gulf Stream waters off the East Coast. False killer whales have been observed off the U.S. West Coast as far north as British Columbia, Canada, typically during warmer oceanographic regimes.
Learn more about the three populations of false killer whales in Hawaiʻi
World map providing approximate representation of the false killer whale range.
Lifespan & Reproduction
The oldest estimated age of false killer whales (based on growth layers in teeth) is 63 years for females and 58 years for males.
Female false killer whales reach sexual maturity between the ages of 8 and 11, while males mature 8 to 10 years later. Gestation ranges from 11 to 16 months, and lactation occurs for 1.5 to 2 years. Time between births is unknown, but is estimated to be around 7 years. Female false killer whales enter menopause and become less reproductively successful between 44 and 55 years old.
Threats
Fishery Interactions
Fishery interactions occur when false killer whales take (or depredate) bait and catch off fishing lines. This action can result in incidental take—unintentional hooking and/or entanglement—as well as serious injury and/or death. False killer whales in Hawaiʻi, particularly main Hawaiian Islands insular false killer whales, have a high rate of dorsal fin injuries and mouthline injuries, likely caused by efforts to take bait and catch from fishing lines.
Competition with Fisheries
Prey items for false killer whales are similar to many of the same species that fisheries target. This is particularly true in Hawaiʻi, where preferred fish for both false killer whales and consumers are tuna, billfish, wahoo, and mahimahi. Competition with fisheries can result in smaller and fewer prey for false killer whales, requiring them to spend more time and energy hunting for food.
Environmental Contaminants
False killer whales are long-lived, upper-trophic-level predators (that is, they’re near the top of the food chain), so they accumulate high levels of toxins from the marine environment. Exposure to toxic chemicals in the marine environment, including persistent organic pollutants (industrial chemicals and pesticides, heavy metals, etc.), can result in a number of biological effects to marine mammals, such as diseases and reproductive issues. It can also affect the quality and quantity of false killer whales’ prey. Although the United States has banned many of these chemicals, some continue to be used in other regions of the world and can be transported via atmospheric means or ocean currents.
Small Population Size
The small size of the endangered main Hawaiian Islands insular false killer whale population poses a unique threat to this group. Within a small, highly social population, the potential for reduced genetic diversity increases, potentially making the population more vulnerable to diseases or other environmental changes. Such environmental events may further harm the population by causing a genetic bottleneck—a reduction in the variation of the gene pool that only rebounds when the population breeds with other populations or enough random genetic mutations have accumulated over many generations. Such a small population may also suffer from a breakdown of cooperative feeding if an aggregation is not large enough to find adequate food.
Hunting
False killer whales are hunted in other parts of the world, including Indonesia, Japan, and the West Indies.
Scientific Classification
| Kingdom | Animalia | Phylum | Chordata | Class | Mammalia | Order | Cetacea | Family | Delphinidae | Genus | Pseudorca | Species | crassidens |
|---|
What We Do
Conservation & Management
We are committed to conserving and protecting all populations of false killer whales. We are especially committed to protecting populations in Hawaiʻi, including recovering the endangered main Hawaiian Islands insular false killer whale. Our work to protect and conserve this species includes:
- Establishing a take reduction team and publishing a take reduction plan to reduce bycatch of Hawaiian false killer whales in commercial longline fisheries.
- Listing the main Hawaiian Islands insular false killer whale as an endangered DPS under the ESA
- Developing a rule to designate critical habitat for the main Hawaiian Islands insular false killer whale.
- Developing a recovery plan and implementation strategy to conserve and recover the main Hawaiian Islands insular false killer whale.
Science
We conduct various research activities on the biology, genetics, behavior, and ecology of false killer whales, with an emphasis on populations of the species in Hawaiʻi. The results of this research inform management decisions for all false killer whales and enhance recovery efforts for the endangered main Hawaiian Islands insular false killer whale DPS. Our work includes:
- Performing stock assessments to gather population information.
- Researching false killer whale social structure.
- Collaborating with scientists to track the movements and behavior of Hawaiian false killer whales.
- Identifying high-use areas of habitat in the main Hawaiian Islands.
- Acoustically monitoring the Hawaiʻi-based longline fishery for interactions with false killer whales.Conducting necropsies on stranded false killer whales.
How You Can Help
Do Not Interact with Marine Animals in the Wild
Do not harass, feed, hunt, capture, kill, pursue, approach, surround, swim with, or attempt to touch protected marine wildlife. Never entice protected marine wildlife to approach you.
Do not engage, chase, or try to get a reaction from the animal. If you’re in the water, allow them to pass without disturbing it. Disturbing wildlife interrupts their ability to perform critical functions such as feeding, breeding, nursing, resting, and socializing.
If you’re on a vessel and a spinner dolphin approaches you, put the engine in neutral and allow the animal to continue on its way. If a spinner dolphin is crossing your path, slow down and pass behind it.
Keep Your Distance
Be responsible when viewing marine life in the wild. Observe all small whales from a safe distance of at least 100 yards and limit your time spent observing to 30 minutes or less.
Report Marine Life in Distress
Report a sick, injured, entangled, stranded, or dead animal to make sure professional responders and scientists know about it and can take appropriate action. Numerous organizations around the country are trained and ready to respond. Never approach or try to save an injured or entangled animal yourself—it can be dangerous to both the animal and you.
Learn who you should contact when you encounter a stranded or injured marine animal
Report a Violation
Call the NOAA Fisheries Enforcement Hotline at (800) 853-1964 to report a federal marine resource violation. This hotline is available 24 hours a day, 7 days a week for anyone in the United States.
You may also contact your closest NOAA Office of Law Enforcement field office during regular business hours.
Featured News
Management Overview
All false killer whales are protected under the Marine Mammal Protection Act. The main Hawaiian Islands insular false killer whale is protected under both the Endangered Species Act and the MMPA. NOAA Fisheries has taken steps to reduce incidental serious injury and death of false killer whales in the Hawaiʻi-based deep-set and shallow-set longline commercial fisheries. NOAA Fisheries has also proposed to designate critical habitat for the endangered main Hawaiian Islands insular false killer whale, with plans to finalize the designation in summer 2018. A recovery plan for ways to recover the endangered main Hawaiian Islands insular false killer whale is also under development.
Recovery Planning and Implementation
Recovery Action
Under the ESA, NOAA Fisheries is required to develop and implement recovery plans for the conservation and survival of listed species. We are committed to the protection and recovery of the main Hawaiian Islands insular false killer whale, with the ultimate goal of helping this distinct population segment recover from its very low population size. This would allow the population to be reclassified from “endangered” to “threatened” and ultimately removed from the list of protected species.
Although we are still drafting the recovery plan, it will recommend the following major actions:
- Determine population trends and continue satellite tagging and photo-identification efforts.
- Conduct fishing gear tests to understand how, why, and from which fisheries injuries are occurring so we can reduce or eliminate injury and mortality caused by fisheries and fishing gear.
- Establish and implement a state of Hawaiʻi non-commercial fishing license.
- Target outreach and awareness to specific fishermen, boaters, and tour operators to effectively mitigate or reduce interactions with false killer whales.
- Acquire biopsy samples to better understand types and effects from environmental contaminants.
- Protect, maintain, and enhance habitat.
Recovery Outline
The ESA mandates that NOAA Fisheries develop and implement recovery plans for the conservation and survival of ESA-listed species under its jurisdiction. We developed a recovery outline (PDF, 23 pages) to systematically and cohesively guide recovery actions for the main Hawaiian Islands insular false killer whale until we complete a recovery plan.
Recovery Planning Workshop
On October 25–28, 2016, we held a recovery planning workshop for the main Hawaiian Islands insular false killer whale. The purpose of the workshop was to review and update the original threats analysis from the 2012 final listing rule and the 2010 Status Review Report, as well as identify potential recovery criteria and actions to address the threats to the main Hawaiian Islands insular false killer whale. Participants included federal and state agencies, scientific experts, commercial and recreational fishermen, conservation partners, and nongovernmental organizations.
- Recovery Planning Workshop Agenda (PDF, 7 pages)
- Main Hawaiian Islands Insular False Killer Whale Recovery Outline (PDF, 23 pages)
- Recovery Planning Workshop Summary (PDF, 27 pages)
Recovery Plan Preparation
In addition to using recovery planning guidance, we are using a new approach developed by the U.S. Fish and Wildlife Service and recently endorsed by NOAA Fisheries. The strategy, briefly described below, will make recovery planning more efficient and effective and to create a more dynamic and flexible plan, presented in two independent parts—a species status assessment and the recovery plan—so it can more easily be updated.
Species Status Assessment
Using the 2010 Status Review Report for the main Hawaiian Islands insular false killer whale as a foundation, we are developing an up-to-date species status assessment. A species status assessment is a stand-alone document that summarizes the status of the species and can be updated as necessary with new information and used for various purposes, including 5-year reviews, section 7 analyses, and section 10 conservation plans. Traditionally, this information was included in the background of a recovery plan and became outdated quickly. As a stand-alone living document, information can be kept more relevant.
Recovery Plan
We are currently drafting a recovery plan for the main Hawaiian Islands insular false killer whale. The three statutory elements required in a recovery plan will be contained in this second stand-alone document:
- Objective, measurable recovery criteria.
- A description of site-specific management actions necessary to conserve the species.
- Estimates of the time and costs required to achieve the plan’s goals.
In addition, a brief introduction to the plan will describe its vision (what the recovered species looks like) and strategy (the rationale for, and how we plan to get to a recovered state). This introduction will provide the trail of logic for recovery and reference the species status assessment.
The draft species status assessment and draft recovery plan will undergo peer review as well as public review and comment before being finalized.
Learn more about the recovery of species under the Endangered Species Act
Critical Habitat Designation
On July 24, 2018, NOAA Fisheries published a final rule to designate critical habitat under the ESA for main Hawaiian Islands insular false killer whales in waters from 45 meters to 3,200 meters (49 to 3,500 yards) in depth surrounding the main Hawaiian Islands (from Ni‘ihau to Hawai‘i Island). This designation does not include most bays, harbors, or coastal in-water structures. Within this larger area, NOAA Fisheries excluded 10 areas from the designation due to economic and national security impacts. In addition, two areas are ineligible for designation because they are managed under the Joint Base Pearl Harbor-Hickam Integrated Natural Resources Management Plan that was found to benefit main Hawaiian Islands insular false killer whales. The total area includes approximately 49,948 km² (19,280 mi²) of marine habitat.
A false killer whale, observed during the 2017 Hawaiian Islands Cetacean and Ecosystem Assessment Survey. Photo: NOAA Pacific Islands Fisheries Science Center/Charlotte Boyd.
Conservation Efforts
Reducing Interactions with Fishing Gear
Bycatch in fishing gear is a leading cause of false killer whale deaths and injuries. To reduce deaths and serious injuries of false killer whales from Hawaii-based deep-set and shallow-set longline fisheries, NOAA Fisheries established a take reduction team. We then published a final take reduction plan and final rule to implement the plan in 2012, based on the take reduction team's recommendations. The final rule includes gear requirements (“weak” circle hooks and strong branch lines) in the deep-set longline fishery, longline fishing closure areas, training and certification for vessel owners and captains in marine mammal handling and release, captains’ supervision of marine mammal handling and release, and posting of placards on longline vessels to aid in species identification and handling and release techniques. We also develop research priorities to support the plan’s implementation and inform development of potential future amendments, and we monitor its progress toward achieving MMPA goals.
Learn more about the False Killer Whale Take Reduction Plan
False killer whales are classified as data deficient on the IUCN Red List of Threatened Species. NOAA Fisheries funds several research studies on life history and stock structure of false killer whales in Hawaiʻi.
Partnering with the State of Hawaiʻi
NOAA Fisheries partners with the State of Hawaiʻi Department of Land and Natural Resources’ Department of Aquatic Resources to undertake cooperative conservation and long-term management of the endangered main Hawaiian Islands insular false killer whale. Our objectives include:
- Conducting field work to address false killer whales’ spatial and temporal habitat use.
- Analyzing overlap between false killer whales and Hawaiʻi state fisheries.
- Investigating strandings.
- Providing targeted outreach to specific fishers, boaters, and tour operators to mitigate or reduce interactions with false killer whales, improve species identification to complement research, and increase public reporting of strandings.
These efforts are funded in part via an ESA section 6 cooperative agreement grant.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes identify strandings due to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
Learn more about the Marine Mammal Health and Stranding Response Program
Regulatory History
False Killer Whale Populations Managed under the MMPA
All false killer whales that reside in the United States are protected under the MMPA. Although there are three populations or stocks of false killer whales in Hawaiian waters, only the main Hawaiian Islands insular false killer whale is listed as depleted (i.e., they have fallen below their optimum sustainable population level). Under the MMPA, the False Killer Whale Take Reduction Plan addresses the threat of incidental serious injury and death of false killer whales in the Hawaiʻi-based deep-set and shallow-set longline fisheries.
False Killer Whale Populations Managed under the ESA
The main Hawaiian Islands insular false killer whale is the only false killer whale population protected under the ESA.
In 2009, NOAA Fisheries received a petition [PDF, 29 pages] to list the Main Hawaiian Islands insular false killer whale as an endangered species and designate critical habitat under the ESA.
NOAA Fisheries reviewed the petition and determined that a status review for the Main Hawaiian Islands insular false killer whale should be conducted.
On November 17, 2010, NOAA Fisheries completed a status review of the Main Hawaiian Islands insular false killer whale and proposed to list it as an endangered DPS under the ESA. Read the ESA status review report.
On November 28, 2012, NOAA Fisheries published a final rule listing the Main Hawaiian Islands insular false killer whale as an endangered DPS under the ESA.
In August 2018, NOAA Fisheries published a final rule to designate critical habitat under the ESA for the main Hawaiian Islands insular false killer whale in waters from 45 meters to 3,200 meters in depth surrounding the main Hawaiian Islands (from Niʻihau to Hawaiʻi Island).
NOAA Fisheries is developing a recovery plan to identify actions that will protect the main Hawaiian Islands insular false killer whale.
Key Actions and Documents
Incidental Take Authorization: Scripps Institute of Oceanography Low-Energy Geophysical Survey in the South Atlantic Ocean
NOAA Fisheries has issued an incidental harassment authorization (IHA) to the Scripps Institute of Oceanography (SIO) to incidentally harass, by Level B harassment only, marine mammals during a low-energy marine geophysical survey in the South Atlantic…
Effective
11/03/2019
Incidental Take Authorization: Low-Energy Geophysical Survey in the Southwest Atlantic Ocean
NOAA Fisheries issued an incidental harassment authorization (IHA) to the Scripps Institute of Oceanography (SIO) to incidentally harass, by Level A and Level B harassment, marine mammals during a low-energy marine geophysical survey in the Southwest…
Effective
09/12/2019
Incidental Take Authorization: Lamont-Doherty Earth Observatory Marine Geophysical Survey in the Northeast Pacific Ocean
NOAA Fisheries has issued an incidental harassment authorization (IHA) to Lamont-Doherty Earth Observatory (L-DEO) to incidentally harass, by Level A and Level B harassment, marine mammals during seismic activities associated with a marine geophysical…
Published
06/10/2019
Incidental Take Authorization: U.S. Navy Hawaii-Southern California Training and Testing (HSTT) (2018-2023)
NOAA Fisheries has received a request from the U.S. Navy (Navy) to extend the expiration date from December 2023 to December 2025 for Marine Mammal Protection Act (MMPA) regulations authorizing the take of marine mammals incidental to Navy training and…
Effective
12/21/2018
Science Overview
NOAA Fisheries conducts research on the biology, behavior, ecology, and genetics of false killer whales, with a special focus on Hawaiian false killer whales. We use the results of this research to inform management decisions, further direct scientific research, and enhance conservation and recovery efforts for the species.
In collaboration with fishermen of the Hawaiʻi longline deep-set fishery, we conduct research to investigate interactions between false killer whales and fishing gear. We deploy small, autonomous acoustic recorders on longline fishing gear to acoustically monitor fishing sets for the presence of false killer whales. We compare the acoustic presence of false killer whales to fishing activity and depredation rates to assess vessel and gear sounds and false killer whale occurrence and behavior around gear, as well as to identify potential acoustic cues.
Visual Observations
We collect observations of whales and dolphins following line-transect protocols. Observers continuously search for animals using 25x150 "big-eye" binoculars to scan 180° forward of the ship. When they spot whales or dolphins, the visual team identifies the species and each observer independently estimates the number of animals in the group.
The notches on the trailing edge of the dorsal fin of the false killer whale on the right form a unique pattern, allowing this individual to be identified each time it is photographed. Photo: NOAA Fisheries.
Passive Acoustic Surveys
Sound travels much farther in water than light, and cetaceans commonly use sound rather than vision to communicate with each other and find food. Just as cetaceans listen for each other and for their prey, we can listen to their sounds to locate groups of whales and dolphins.
Unmanned Aircraft Systems
Target species for Unmanned Aircraft Systems operations include false killer whales, short-finned pilot whales, sperm whales, and Bryde’s whales. We may also conduct flights during sightings of rare and high-profile species, such as killer whales, blue whales, and North Pacific right whales, to maximize the information gained from such unique opportunities.
Surveying with Drifting Autonomous Spar Buoy Recorders
We’ve broadly used autonomous (no human intervention needed) stationary acoustic recorders to understand the distribution and seasonality of cetaceans throughout the world’s oceans. Our scientists maintain a network of seafloor-anchored passive acoustic listening stations to listen for cetaceans and understand ocean noise.
Identifying "Mystery Whales" Using Environmental DNA
The name eDNA derives from the collection method—essentially, we are detecting the DNA of an individual as it passes through the environment and sheds small bits of tissue, such as sloughed skin.
Ocean Noise Reference Stations
To monitor ocean noise, NOAA has deployed acoustic monitoring stations throughout U.S. waters that together make up the Ocean Noise Reference Station Network. One of these stations is located approximately 100 miles north of Oʻahu.
Marine Mammal Unusual Mortality Events
Under the Marine Mammal Protection Act, an unusual mortality event (UME) is defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response." To understand the health of marine mammal populations, scientists study unusual mortality events.
