Speculation that a great white shark that went missing off Australia may have been devoured by another great white is making the Internet rounds this week, raising the question of whether it was an instance of shark cannibalism.
The shark that disappeared was wearing a research tag, which a beachcomber found 2.5 miles (four kilometers) away from where it had been affixed to the shark.
The tag, initially attached in November 2003 off southwestern Australia, was set to record ambient temperatures and depth. Its data showed that four months after it was attached, the female great white abruptly dove to a depth of 1,903 feet (580 meters). The ambient temperature surrounding the tag spiked from 46°F to 78°F (8°C to 26°C). The data suggested an attack.
Filmmaker David Riggs, who'd been hired to document the tagging project that involved the nine-foot-long female shark, couldn't believe the data at first.
Clearly something ate the shark, Riggs said in a YouTube clip uploaded by the Smithsonian Channel a couple of weeks ago. A reddit user posted the video on the popular site this week, and it quickly went viral. But "what could kill a three-meter great white?" Riggs asked. (See "Scientists Track a Great White Shark Across the Atlantic for the First Time.")
The search for the perpetrator is the subject of a Smithsonian Channel show airing later this month.
Cannibalism Is Common
Experts say that speculation that a great white devoured the missing female great white is not outside the realm of possibility.
"Cannibalism in sharks is quite common in both juveniles and adults," said Camrin Braun, a doctoral student at the Woods Hole Oceanographic Institution in Massachusetts who studies shark population and behavior. White sharks in particular have highly variable diets, he added in an email interview, and are likely opportunistic when it comes to finding food.
But a more likely explanation for the surprising tagging data, said Braun, is that the female great white got caught in the crosshairs of a killer whale.
"White shark stomach temperatures are thought to be on the order of 65 to 70°F," he explained. "Maybe even less at great depth in cold water." That's cooler than the temperature recorded on the tag.
The only other animal that could take on a small great white—and that has a warmer ambient internal temperature—is the killer whale, Braun said. Their internal temperatures run about 90°F (32°C), he explained. "Thus, it seems likely that a feeding killer whale that is ingesting cold seawater and food could easily have a stomach temperature of 78°F."
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