Frequently asked questions about the process of investigating marine mammal strandings involving dead animals.
A necropsy is the examination of the dead body or carcass of an animal, similar to an autopsy conducted on humans.
Scientists and veterinarians routinely conduct necropsies of marine mammals as part of a conservation management program. Necropsies of marine mammals (e.g., seals, sea lions, dolphins, and whales) can provide significant information regarding the health of the individual animal, the species, and the ocean environment.
NOAA Fisheries’ Marine Mammal Health and Stranding Response Program oversees and authorizes highly skilled and trained members of the National Marine Mammal Stranding Response Network to respond to stranded marine mammals and conduct necropsies to investigate causes of death. The Network is made up of more than 120 professional organizations, including local, state, tribal, and federal government agencies, zoos and aquaria, veterinary clinics, non-profit organizations, and academic institutions.
Marine mammal carcasses may strand or come ashore in a variety of places, including remote islands, on protected lands, or private lands. Carcasses can also be found floating in the ocean, and may be towed to shore for examination or examined at sea.
The Network responds, when safe and feasible, to document and recover carcasses. It does not and cannot respond to every stranded marine mammal, and is not responsible for disposing of carcasses.
The type of examination conducted varies and depends on availability of resources, location, carcass accessibility, and the decomposition state. If the animal is too large to move (e.g., baleen whales), exams are done in the field, which could be on the beach, shore, or at sea. Smaller animals—such as seals, sea lions, dolphins, and porpoises—may be examined in a laboratory or necropsy room at a Network or partner facility.
Necropsies on large animals, such as whales, are resource intensive. They may require heavy machinery such as front loaders and excavators to move larger animals to a safer location and to help position the animal for better examination.
Animals may have been exposed to harmful contaminants or carry diseases that are transmissible from the animal to humans. Necropsy team members often wear personal protective equipment such as gloves, gowns, or aprons to prevent excessive exposure to the carcass.
They work in close proximity with one another and must be mindful of their surroundings to avoid injury. Necropsy teams work with a variety of sharp cutting tools, such as knives and scalpels, and ropes that are often under heavy tension when recovering a carcass in the surf or manipulating it for examination.
Given these potential human safety risks, and the required space needed for necropsy teams to operate on the beach, teams often establish a safety perimeter for the public around the necropsy area.
Team members often collect biological samples from many parts of the animal. These include skin, blubber, muscle, baleen/teeth, and internal organs. These samples help us understand marine mammal biology, pathology, and sometimes cause of death.
Strandings sometimes involve human interactions, such as vessel strikes, entanglements, gunshots, or pollution, such as oil spills or other toxic chemicals. In those cases, samples may need to be collected according to specific “Chain of Custody” protocols to support law enforcement investigations.
Acoustic trauma, which could result from close exposure to loud human-produced sounds, is very challenging to assess, particularly with any amount of decomposition. Scientists look for bruising or trauma to the ear and other organs, but certain parts of the ear decompose very quickly (within hours), and linking findings to a particular sound source is difficult.
A necropsy involves visually examining the carcass, both externally and internally, evaluating samples by microscopic analyses, and a variety of other laboratory based tests—the results from necropsies are rarely (if ever) immediate.
Necropsy teams may have preliminary information on the animal’s health status based on the initial visual exam. But, the information will often need to be confirmed by diagnostic laboratories that use microscopes, genetic and pathogen testing, and other techniques to better verify what the necropsy team documented in the field.
There may be multiple health concerns noted during the examination. A necropsy report, when written, includes data which are compiled over several weeks to months, and then analyzed for a possible cause of death determination and findings.
Multiple experts are often needed to ground truth findings. This is similar to how people get additional opinions from doctors to confirm a diagnosis or medical course of action.
Necropsy results, once finalized, are used to inform managers, scientists, and other stakeholders.
The monetary and in-kind costs associated with a marine mammal necropsy are typically covered by the individual Stranding Network organization that conducts the response. In some situations, such as during Unusual Mortality Event investigations, partners may receive some additional monetary support from NOAA Fisheries. Our Stranding Network partners may also receive some monetary support through the John H. Prescott Marine Mammal Rescue Assistance Grant Program. Stranding Network organizations also receive some assistance (logistical and in-kind) from local jurisdictions, including towns, cities, and counties, that often assist with moving and disposing of large animals.
The Marine Mammal Protection Act authorizes emergency response to marine mammal species and data and sample collection through formal stranding agreements issued to the Stranding Network. However, it does not mandate conducting necropsies. NOAA Fisheries does not require Stranding Network partners to conduct stranding responses or necropsies for every case, as a response may not always be safe or logistically feasible (i.e., carcasses may be in an inaccessible location that would make a necropsy unsafe and/or logistically challenging). Similarly, our Stranding Network partners are not required to dispose of all marine mammal carcasses in their area, but do follow marine mammal carcass disposal best practices when they conduct disposal activities.
Level A data represent basic information on the stranding event, including:
The Level A form records whether a necropsy was conducted and if samples were taken for purposes including diagnostics and research, but does not collect the results of these analyses. Level A data is considered public information and may be released upon written request to NOAA Fisheries.
These data represent supplemental information about the stranding event, the life history of the animal (reproductive status, food habits, etc.), and the results of any analyses of tissues for purposes such as identification of infectious disease, toxins, or parasites. Collection of Level B and C data are not mandatory since their collection requires considerable extra effort and resources that are not always readily available. Further, collection of these types of information is highly variable depending on the species, level of examination, state of decomposition, and other factors. Sharing this information has been at the discretion of individual Stranding Network participants that collected the data or performed the analyses.
Amendments to the Marine Mammal Protection Act enacted in 2022 will change the sharing of Level B and C data. In the future, some Level B and C data will be required to be submitted to a government database and will be made publicly available. This database is under development and, given the complexity, will take several years to complete. Once it is complete, submitting some Level B and C data from necropsies will be required (starting as early as 2026). The requirement will only apply to future cases, not retrospectively.
If you come across a stranded marine mammal, remain a safe and legal distance from the animal. Immediately report any injured, entangled, or dead whales, seals, sea lions, dolphins or porpoises to your regional 24/7 hotline. The quality of necropsy results can depend on the amount of decomposition in the animal, so timely reporting may allow Network members to conduct a necropsy before a carcass decomposes too much.
The most important information to collect is the date, location of stranding (including latitude and longitude), number of animals, whether the animal is alive or dead, and species, if known.
Photos or videos (from a safe and legal distance) can also provide valuable information to Network responders. You can also download the Dolphin and Whale 911 Stranding App to report the stranding.
A stranding responder measures a stranded loggerhead sea turtle on a Florida beach. Photo credit: Florida Sea Turtle Stranding and Salvage Network
Pair of bottlenose dolphins. Credit: NOAA Pacific Islands Fisheries Science Center/Lisa Morse.
