When a whale dies, its body sinks, floats or washes ashore. If it reaches the deep seafloor, it becomes a “whale fall”. Sharks and hagfish strip the meat, worms move in, and then bacteria feed on the fat in the bones for 50 years or more, according to a review by Smith and Baco (2003).
How do whales die?
Whales die of many of the same things as other animals. NOAA Fisheries lists the common causes of strandings as disease and infections, parasites, starvation, harmful algae, cancer and unusual weather. People cause deaths too, mainly through ship strikes and tangling in fishing gear.
Some deaths are natural in a very Arctic way. NAMMCO reports that ice has trapped and killed 40 blue whales in the Northwest Atlantic since 1974. Big whales also die of old age; blue whales can live at least 80 to 90 years.
Predators kill some whales, mostly young ones. Killer whales are the main hunter of large whales. You can read how they do it in what eats a blue whale and what eats a humpback whale.
Do dead whales sink or float?
Both happen. A dead whale may float, or it may sink and then bob back up later, explain Moore and colleagues (2020), writing for NOAA’s stranding program. It depends on gas.
After death, bacteria inside the body keep breaking down tissue and make gas. The gas is trapped under thick blubber, so the body swells like a balloon. In warm, shallow water, that gas can lift a sunken whale back to the surface. In cold, deep water, the high pressure squeezes the gas, so the carcass may never come back up.
That is why most dead whales are never found. Only some float or wash ashore. Many sink out of sight and stay on the seafloor.
What happens when a whale dies on a beach?
A whale found dead on the shore, or alive and unable to swim back, is called a stranding. NOAA Fisheries says thousands of stranded marine animals are reported to stranding networks each year.
Trained teams then do a necropsy, which is an autopsy for animals. They take samples of skin, blubber, muscle and organs to find out why the whale died. For a big whale, the work happens on the beach, often with diggers and loaders to move the body, says NOAA’s necropsy page. Speed matters, because a rotting carcass holds fewer clues.
If you find a stranded whale, stay back and keep others away. Do not touch it. Dead animals can carry diseases and harmful chemicals. Call your local stranding network, or use the Dolphin and Whale 911 app in the United States. It is also illegal in the US for the public to handle stranded marine mammals without permission.
What is a whale fall?
A whale fall is a whale carcass on the deep seafloor. For animals down there, food is usually scarce. A dead whale is a sudden feast. Large whales weigh 30 to 160 tonnes as adults, Smith and Baco note, and all of it becomes food.
Scientists have watched whale falls change over time, mostly off California. Some whales were found by chance. Others were sunk on purpose after they had washed ashore, so researchers could return again and again. They found that a whale fall passes through overlapping stages.
| Stage | What happens | Main animals | How long |
|---|---|---|---|
| 1. Mobile scavengers | Soft tissue is eaten at about 40–60 kg (90–130 lb) a day | Sleeper sharks, hagfish, rat-tail fish, crabs | About 4 months to 2 years; perhaps 5 years for a 100-tonne blue whale |
| 2. Enrichment opportunists | Worms and snails crowd the bones and the rich mud around them | Bristle worms, crustaceans; up to 45,000 animals per m² | Months to about 2 years |
| 3. Sulphur-loving stage | Bacteria break down fat inside the bones and release sulphide, feeding mats of bacteria, clams and mussels | Bacteria, mussels, clams, limpets, snails | Decades; at least 50 years for big skeletons |
| 4. Reef stage | Once the food is gone, the bones may act as a hard “reef” for animals that filter food from the water | Filter feeders | Not well studied |
Durations and species come from Smith and Baco (2003), and the worm count comes from MBARI. The 5-year figure for a blue whale is an estimate, not a measurement.
What eats a dead whale?
First come the big scavengers. On one 35,000 kg carcass off California, researchers counted 400 to 800 hagfish after about six weeks, report Smith and Baco. Pacific sleeper sharks, rat-tail fish and crabs join in. Together they can strip most of the flesh.
Then come the strangest guests. In February 2002, MBARI scientists found a dead whale 2,891 m deep in Monterey Canyon, California. Its bones were covered in red worms 2 to 7 cm long. The worms, named Osedax, have no eyes, legs, mouths or stomachs, says MBARI. Green roots grow into the bone, and bacteria inside them break down the oil.
Floating carcasses get eaten too. In South Africa, up to 40 white sharks a day were seen feeding on dead whales, reports a 2013 PLOS ONE study by Fallows and colleagues. The sharks preferred the fatty blubber. Only 19 such scavenging events had been published since 1896. See how great white sharks are adapted for more on these hunters.
Why are whale falls important?
They are islands of life on a dark, food-poor seafloor. Smith and Baco counted 407 species at whale falls worldwide. Large skeletons in the sulphur-loving stage held an average of 185 species of small animals each. That is more than any other deep-sea hard surface they compared.
At least 21 species are known only from whale falls. Whale falls also share species with hot-water vents and cold seeps, other places where life runs on chemicals, not sunlight. MBARI reports that whale falls may lie roughly every 5 to 16 km along the seafloor. That may be close enough for larvae to drift from one to the next, like stepping stones.
The bones are rich in fat. The skeleton of a 40-tonne whale may hold 2,000 to 3,000 kg of fat, Smith and Baco estimate. That is why the last stage can last for decades. To picture how big the largest whales are, see how big a blue whale is.
Frequently asked questions
How long does a whale fall last?
A large whale fall can feed animals for 50 years or more. Scavengers remove the flesh in months to a few years, depending on the size of the whale. Bacteria then feed on the fat in the bones for decades, according to Smith and Baco (2003).
What are zombie worms?
They are bone-eating worms called Osedax, first found by MBARI on a dead whale in Monterey Canyon in 2002. They are 2 to 7 cm long and have no mouth or stomach. Roots grow into the bone, and bacteria in them digest its oil.
Is it safe to touch a dead whale?
No. Stay back and keep pets away. Dead marine mammals can carry diseases and harmful chemicals, says NOAA Fisheries. Report it to your local stranding network instead, so trained responders can examine it and find out why it died.
Why do dead whales swell up?
Bacteria inside the body keep breaking down tissue after death and give off gas. Thick blubber traps the gas, so the carcass swells. In warm, shallow water the gas can even lift a sunken whale back to the surface, Moore and colleagues explain.
Sources
- University of Hawaii (author copy) (2003). Ecology of whale falls at the deep-sea floor (Smith & Baco, Oceanography and Marine Biology: An Annual Review 41: 311–354).
- MBARI (2002). Whale falls: islands of abundance and diversity in the deep sea.
- MBARI (2004). Whale carcass yields bone-devouring worms.
- NOAA Institutional Repository (2020). Dead cetacean? Beach, bloat, float, sink (Moore et al., Frontiers in Marine Science, doi:10.3389/fmars.2020.00333).
- NOAA Fisheries. Understanding marine wildlife stranding and response.
- NOAA Fisheries. Frequent questions: necropsies (animal autopsies) of marine mammals.
- PLOS ONE (2013). White sharks scavenging on whales and its potential role in further shaping the ecology of an apex predator (Fallows et al., doi:10.1371/journal.pone.0060797).
- NAMMCO. Blue whale.
Sources checked 15 September 2026.
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