Making sense of strandings

When a marine mammal washes ashore, the forensic investigation begins. How did the animal become stranded? What can it teach us about the health of its ocean habitat? As a member of the Marine Mammal Stranding Network, a federal rescue and research program led by the National Marine Fisheries Service, the Academy responds to strandings along our coast to better understand why the animals washed ashore—and help reduce the frequency of such events in the future.

From Año Nuevo in the south to mid-Mendocino in the north, whenever a deceased marine mammal is reported, responders from the Academy’s Department of Ornithology and Mammalogy spring into action. They locate the specimen, take measurements, and depending on the condition of the animal perform an examination known as a necropsy (or animal autopsy) to collect tissue and bone samples that help determine the animal’s cause of death. After being processed, these samples are added to the Academy’s scientific collection, providing data for researchers from around the world seeking to better understand and protect our ocean’s increasingly vulnerable marine mammals.

It is illegal to approach or handle a sick or injured marine mammal or collect any parts of dead marine mammals. If you encounter a sick or injured marine mammal, call The Marine Mammal Center at 415-289-SEAL. If you encounter a dead marine mammal, call the Academy at 415-379-5381 or email marinemammals@calacademy.org. For more information, view the FAQ below.

Investigating die-offs

In an average year, an estimated four to five gray whales are expected to wash ashore in the Bay Area. Since 2019, there have been more than two dozen. This uptick, which has been happening along the entire Pacific coast of North America, led the National Oceanic and Atmospheric Administration (NOAA) to declare the mass die-off an unusual mortality event (UME) and launch a formal investigation into the cause.

As one of the investigation's state representatives, Academy Senior Collections Manager Moe Flannery is helping lead efforts to collect data from each stranding to determine cause of death and, ultimately, what can be done to protect the beleaguered species.

But it’s not only gray whales that the Academy is helping to protect. In 2015, after a notable uptick in the number of threatened Guadalupe fur seals washing up onto Bay Area beaches, the Academy response team alerted NOAA who declared a UME for the species, thus mobilizing additional resources to investigate the strandings.

Similar efforts in the past from the Academy and other members of the Marine Mammal Stranding Network have successfully led to policy changes in San Francisco Bay, although more research and advocacy is needed.

Scenes from a stranding

From getting to the scene to dissecting the mammal to cataloging the samples, conducting necropsies is grueling work. But the trove of information they provide for scientists is an invaluable resource for understanding and protecting marine mammal species.

A general whale necropsy performed by the Academy and The Marine Mammal Center includes the following steps:

  1. Evaluate the external state of the animal to look for signs of injury such as lacerations or missing parts.
  2. Extract tissue and bone samples by cutting into the animal to assess life history, age, and health. For example, teeth or baleen—a comb-like structure some whales use to filter-feed—can be used to determine the age of the animal and fractured bones can be evidence of blunt force trauma, often from being struck by a boat.
  3. Process samples of the animal. Smaller bones are typically treated by maceration—a process that involves soaking them in water where bacteria break down any remaining tissue. Larger bones are placed on the Academy's Living Roof where they are “cleaned” by bacteria in the soil and the Sun’s ultraviolet radiation.
  4. Add samples to the Academy’s collections so scientific researchers around the world can analyze them to identify toxins in the animal’s body and diet, when the animal last gave birth, its stress levels, and more.
  • Academy scientists conduct a necropsy on a stranded whale
    Each necropsied whale harbors important information about the overall health of the Bay Area's marine mammals.
  • Moe Flannery examines a stranded pinniped on the beach
    Biologist Moe Flannery, who leads the Academy's efforts as part of NOAA's Marine Mammal Stranding Network, examines a deceased pinniped.
  • Sue Pemberton collects a skull from a dead seal on the beach
    Academy Stranding Coordinator Sue Pemberton collects a skull from a seal which, once processed, will be added to the Academy’s collection.
  • Scientists collect samples from a stranded fin whale in Stinson Beach in 2013. Photo by Diana Humple
    The Academy's marine mammal response team collects bones, tissue, and other samples from a deceased fin whale to take back to the lab. Photo courtesy of Diana Humple
  • Moe Flannery inspects whale bones on the Academys Living Roof
    Moe Flannery lets the Sun’s UV rays naturally disinfect whale bones on the Living Roof before adding them to the Academy’s scientific collection.

Preventing ship strikes

While seeing whales along the coastline of the Bay Area is an awe-inspiring spectacle, their presence so close to shore sometimes leads to unintentional run-ins with another common sea sighting: ships.

Each year, a number of whales wash up throughout the Bay Area showing signs of trauma that indicate the cetacean was struck by a ship. These ship strikes often occur when a whale surfaces to breathe at the same time a ship passes by. Reducing speeds on the water or adjusting shipping lanes could help prevent these tragic accidents.

Scientists—with help from the public—have been tracking whales and ship strikes along the coast to get a better idea of where those preventive measures could be most effective, and have already influenced policy changes in the waters surrounding San Francisco Bay.

“My hope is that our research will continue to inform policies like the 2013 changes in shipping lanes and the reduction of boat speeds to protect the iconic, yet vulnerable whales along the California coast."
—Moe Flannery, Academy biologist


What should I do if I see an injured or dead marine mammal?

First, do not approach the animal! It is illegal to approach a sick or injured marine mammal or collect any part of a dead marine mammal. You can help, however, by reporting your sighting:

  • If you encounter a sick or injured marine mammal, please contact The Marine Mammal Center at 415-289-SEAL or visit their website.
  • If you encounter a dead marine mammal, please call the California Academy of Sciences' Department of Ornithology and Mammalogy at 415-379-5381 or email marinemammals@calacademy.org.

Try to collect the following information for your dead animal report:

  1. Type of animal: Common sightings include seals, sea lions, whales, dolphins, and otters.
  2. A description of the animal: approximate size, color, and any distinguishing features. Taking photos is helpful and encouraged but please do not touch the animal to do so.
  3. The specific location of the animal: Name of beach and distance from nearest parking lot, road, or trail. Drop a pin using your phone’s map app if possible.
  4. The date and time you saw the animal.
  5. Any other relevant information, along with your name and phone number.
What kinds of marine mammals live in Northern California and San Francisco Bay? 

The California coast hosts one of the most diverse menageries of marine mammals in the world. See below for a breakdown of some of the species you might encounter along the shores of San Francisco Bay and the rest of Northern California:

Pinnipeds (seals and sea lions)

Cetaceans (whales, dolphins, and porpoises)

Mustelids (otters and other carnivores)

Why have there been so many whale strandings?

While the cause of the recent increase in whale strandings is unknown, the Academy and other members of the Marine Mammal Stranding Network are responding to as many reported events as possible to try and find out.

So far, the main causes of death appear to be ship strikes and malnutrition, but investigations and research are ongoing. Learn more about whale strandings here.

What can I do to help? 

Marine mammals aren’t just intelligent and charismatic—they’re critical components of the marine food web, and protecting them is in everyone’s best interest. By staying alert on the water and on shore, choosing sustainable seafood, and reducing your carbon footprint, you can help ensure their survival.

  1. Boat safely. If you’re on a watercraft in the Bay or along the coast, stick to designated lanes of travel and keep your speed low. Always keep an eye out for marine mammals, and observe them from a safe distance—do not approach.
  2. Eat sustainable seafood. Decades of overfishing have reduced marine mammals’ food sources, and improper disposal of fishing gear entangles and kills hundreds of thousands of marine mammals and sea turtles around the world every year. By making smarter choices around the seafood you buy, you can help fish stocks recover and keep marine mammals healthy. Get started by downloading Monterey Bay Aquarium’s Seafood Watch guide.
  3. Reduce your carbon footprint. Climate change caused by the burning of fossil fuels is warming and acidifying our oceans, making it even harder for marine mammals to thrive. By eating less meat, taking fewer plane trips, and limiting your use of plastic, you can help lower your impact on our climate.
  4. Support marine-mammal-friendly policy. Speak up in support of legislation that reduces speed and traffic in and out of major shipping ports.
  5. Report dead or injured marine mammals. Each animal provides valuable data that can inform species conservation and environmental policy. If you encounter a dead marine mammal, contact the California Academy of Sciences at 415-379-5381 or marinemammals@calacademy.org. If you encounter a sick or injured marine mammal, contact The Marine Mammal Center at 415-289-SEAL.
I'm a journalist. How can I reach someone about this topic?

Please direct all press inquiries to press@calacademy.org.

All marine mammals are federally protected by the Marine Mammal Protection Act. Only local and state officials and people authorized by NOAA Fisheries may legally handle live and dead marine mammals. All marine mammal stranding activities depicted above are conducted under authorization by the National Marine Fisheries Service through a stranding agreement issued to the California Academy of Sciences and MMPA/ESA Permit No.18786-01.

Academy Contributors

Moe Flannery, Senior Collection Manager, O&M
Senior Collections Manager, Birds and Mammals
Sue Pemberton
Curatorial Assistant, Birds and Mammals


Report sick, injured, or dead marine mammals

For sick or injured marine mammals, please call The Marine Mammal Center at 415-289-SEAL or visit their website.

For dead marine mammals, please call the Academy's department of Ornithology and Mammalogy at 415-379-5381 or email marinemammals@calacademy.org.


What to include in your report
  1. Type of animal
  2. Description of the animal
  3. Specific location of the animal
  4. Date and time you saw the animal
  5. Other relevant information, along with your name and phone number

For more details, view the FAQ.