In 2003, a research team off the southern coast of Australia attached an electronic tag to a female great white shark. The shark was an adult, roughly nine feet long, and in good health. After tagging, she was released and swam back into open water. Four months later, the tag washed ashore hundreds of kilometers away. When researchers downloaded its data, they found the tag had recorded a rapid temperature spike, followed by a sustained dive into deep water. The readings indicated the shark had been consumed by another animal. The question that followed was which animal could swallow an adult great white shark whole.

The tag used was a pop-up archival transmitting tag, known as a PAT tag. These devices attach to a shark and log depth, temperature, and light levels continuously. They do not transmit data in real time. Instead, they store measurements until a pre-programmed release date, when they detach, float to the surface, and transmit a summary to a satellite. This meant the researchers were always reviewing past events, often months old.

The temperature reading was the first unusual detail. For most of the four months, the tag recorded water temperatures around 7.8 degrees Celsius, matching the cold open-ocean environment. Then, within minutes, the temperature rose sharply to about 25.5 degrees Celsius and remained there for hours. That level of consistent warmth was too high for seawater and matched the internal temperature of a large animal’s digestive tract.

At the same time, the tag recorded a rapid, deliberate descent. It sank past 100 meters, then 200, then 300, reaching roughly 580 meters. The dive was too fast and directed to be a drifting object. It appeared that something had swallowed the shark and carried the tag into deep water.

The tag continued transmitting through the event. It remained at depth for hours while the internal temperature stayed stable, suggesting the animal was digesting its meal. Eventually, the readings changed as the animal moved upward, and the tag was eventually released through the digestive system. It floated to the surface, transmitted its data, and drifted until it landed near Bremer Bay, southeast of Perth.

Researchers ruled out equipment failure. A malfunctioning sensor would typically produce erratic readings, but the temperature and depth data were consistent and mutually reinforcing. Two independent sensors agreed on the sequence of events.

They also ruled out natural death and sinking. A dead shark would cool toward the surrounding water temperature. The data showed warming, not cooling. Only a living, metabolically active animal could produce that kind of sustained internal heat in deep water.

The leading suspect initially was the orca. Orcas are known to kill great white sharks, and documented cases exist of them targeting and removing shark livers off South Africa. However, the data did not match orca behavior. Orcas are mammals with core temperatures around 98 degrees Fahrenheit. The tag recorded a much lower temperature, roughly 78 degrees Fahrenheit. That is too cold for a mammal’s internal body heat.

Orcas also tend to hunt near the surface, where they can maneuver and breathe. The tag showed a complete swallow followed by a deep dive, which is not how orcas typically feed on sharks. They usually remove the liver and leave the rest of the carcass.

The temperature reading pointed to another great white shark. Great white sharks are regional endotherms, meaning they generate some internal heat but run cooler than mammals. Their internal temperature typically sits in the range the tag recorded. They also routinely dive to depths of 500 to 600 meters, matching the dive in the data.

The likely predator was a significantly larger great white shark, estimated at around 16 feet long and weighing more than two tons. Great whites of that size are documented. A female known as Deep Blue, encountered near Mexico’s Guadalupe Island, was estimated at over 20 feet long and around 50 years old.

There is no need to invoke an undiscovered species. Speculation about the megalodon, an ancient shark that went extinct millions of years ago, does not fit the evidence. Megalodon lived in warm coastal waters, not the cold deep ocean where the tag recorded its data.

The more unusual implication is that great white sharks occasionally prey on smaller members of their own species. This behavior is not captured by cameras and is difficult to observe in open water. The tag’s data provided a rare, direct record of such an event. It is not known how often this happens, as most predation events in the deep ocean are never witnessed.