In 2003, researchers tagged a female great white shark off the coast of Western Australia as part of a routine marine research program. The shark, about nine feet long and healthy, was fitted with a data recorder rather than a real-time tracking beacon. Four months later, the device washed ashore roughly 2.5 miles from where it had been deployed. The shark was never found, and the data it contained pointed to an unusual explanation.
The tag recorded depth, temperature, and light levels at regular intervals. For months, it logged a normal pattern of shark behavior along the continental shelf. Then, on the morning of December 24, the device recorded a sudden and violent descent to about 1,900 feet. At that depth, the water off Bremer Bay is typically around 46 degrees Fahrenheit. The tag, however, registered a temperature of 78 degrees shortly after the dive and held that reading for eight consecutive days. During that time, the device continued to move, rising and falling between the surface and roughly 330 feet.
When researchers recovered the tag, its casing showed signs of wear consistent with exposure to stomach acid. The likely conclusion was that the shark had been consumed by a larger animal. No witnesses observed the event, and no camera captured it. The only evidence available was the data stored on the device.
The researchers involved in the tagging program, including filmmakers Dave and Jenine Riggs, who had spent years documenting wildlife along that coastline, were reportedly taken aback by the finding. The central question was straightforward: what could kill and consume a large great white shark?
The great white shark is one of the ocean’s most specialized predators. Large females can reach roughly 20 feet in length and weigh more than 4,000 pounds. They can detect small amounts of blood in water, sense electrical impulses from prey through specialized receptors, and swim at speeds up to 25 miles per hour. They are also partially warm-blooded. A network of blood vessels allows them to retain body heat generated by swimming, keeping their core, eyes, brain, and stomach warmer than the surrounding water.
This last detail became central to the investigation. Researchers considered several possible culprits.
Orcas were an early candidate. They are known to hunt great white sharks in some regions, and there are documented cases of orcas killing white sharks off California and South Africa. However, orcas are warm-blooded mammals with body temperatures around 98.6 degrees. The temperature recorded by the tag, 78 degrees, was lower than would be expected inside an orca. The dive pattern also did not match typical orca hunting behavior.
Sperm whales were considered next. They are deep divers and can reach depths of 3,000 feet or more. But they are also warm-blooded, and their primary prey is squid rather than sharks. The temperature reading again did not align.
Giant squid were ruled out on biological grounds. They are cold-blooded and would not maintain a temperature far above the surrounding water. The suggestion of a surviving megalodon was dismissed on evidentiary grounds, as the species disappeared from the fossil record roughly 3.5 million years ago.
That left a more straightforward possibility: the shark had been eaten by a larger great white shark. Great whites maintain a stomach temperature higher than the surrounding water, though typically not as high as the 78 degrees recorded. Larger animals retain heat better than smaller ones, and some researchers noted that a very large shark could potentially produce a higher internal temperature than smaller specimens tested in previous studies. This point has not been confirmed, and some researchers, including Riggs, have not closed the case entirely.
Cannibalism among sharks is not unprecedented. Some shark species eat their siblings in the womb, and large white sharks have been found with bite marks consistent with encounters with other great whites. In Australian waters, sharks recovered from fishing nets have shown large bites attributed to bigger sharks. A predator large enough to consume a nine-foot shark would likely need to be at least twice its length, suggesting an animal of roughly 16 feet or more. White sharks of that size have been documented in Australian waters, including a specimen estimated at 17 feet tagged off Albany in 2014 and a large female filmed near Guadalupe Island in Mexico.
The broader implications of this event relate to how white shark populations are monitored and protected. Most sharks are tagged near shore, where smaller and younger individuals are more commonly encountered. Large, older sharks, particularly females, spend much of their time farther offshore and are rarely seen. If larger sharks regularly prey on smaller ones, population estimates based on juvenile survival rates could be incomplete.
The event also raises questions about how the term apex predator is applied. In this case, the data suggests that the top of the food chain may be size-dependent rather than fixed. A nine-foot great white was killed by something larger in the same species, and that larger animal was not observed or documented.
The tag that washed ashore at Bremer Bay remains one of the few pieces of evidence that such an interaction occurred. It indicates that large white sharks occasionally hunt other large white sharks, but how often this happens, and at what sizes, remains unknown. The episode has not produced a definitive answer, but it has highlighted how much of the open ocean, particularly at depth, remains unobserved.
