A search for the world's largest mako shark ended with researchers encountering an enormous female off the California coast that may have broken the species' 13-foot ceiling, according to a new Shark Week episode.
The episode, titled 'Biggest Mako on Earth,' airs on the Discovery Channel on Monday at 9pm ET. The expedition was launched after tourists off Cabo San Lucas, Mexico, reported seeing a 15-foot mako that could be the largest ever documented.
Marine biologist Tristan Guttridge and his team searched waters off Mexico and California to determine whether such giants exist. Their breakthrough came at the end of the expedition, when a huge female appeared beside their boat and tore apart a piece of tuna.
The shark circled and thrashed in the water as Guttridge tried to measure it from the vessel. Its exact length could not be confirmed, but the animal appeared about a foot longer than another mako the team had measured at more than 12 feet.
"We didn't get a precise measurement, but it is very possible that last mako broke the 13-foot ceiling," said expert Kendyl Berna. "We suspect there are bigger makos out here. We know there are bigger makos out here."
A monster shadow off Cabo San Lucas
The investigation began off Cabo San Lucas, where a tourism group had entered the water hoping to see blue sharks and makos. Instead, an enormous shadow appeared beneath them, and one witness shouted, "There is a monster down here."
The shark was estimated at 15 feet long, about two feet larger than the largest reliably photographed makos. Clara Calatayud, who witnessed the encounter, later took Guttridge back to the location.
"The team that saw this shark, they've spent time in the water with these, so this was definitely a massive animal," Guttridge said.
Adult makos typically reach around nine feet, and females can grow to 12 feet, though stories of sharks exceeding 13 feet have circulated for decades with little photographic proof. Makos migrate between Mexico and California each year, but confirming a 15-foot specimen would require luring one close enough to the surface for a reliable measurement.
The team dropped bait into the water and quickly attracted several blue sharks, some over six feet long. The mood shifted when a seven-foot mako appeared while Guttridge was in the water.
"The mood completely shifted. The blue sharks know to stay out of the mako's way," he said. It was not the giant they were searching for. A thresher shark was later seen leaping in the distance, but the mako disappeared and Guttridge returned to the boat. After hours of dropping bait with no sign of a giant female, the team moved to the cooler waters around Catalina Island, California.
Testing how much a mako can eat
The team's hopes were fueled partly by a 1952 photograph showing fishermen posing with a shark they claimed measured 19 feet. Shark Week experts believed the animal could have been a giant mako, though its species and size were never confirmed.
Researchers first wanted to know whether makos could physically eat enough to reach 15 feet or more. The sharks burn energy three to six times faster than other species and need at least twice as much food, but no one knew how much a mako could eat in a single feeding.
Berna joined the expedition as the team sourced 500 pounds of tuna for what they called the world's first mako feeding test. "If we find out they are eating more than 10 percent of their body weight in food, this could explain how we could get a 15-foot or maybe even bigger mako," she said.
When the first shark arrived, Guttridge entered a steel cage and used cameras to measure it. The male was about nine feet long and weighed an estimated 500 to 600 pounds, within the average range. The feeding test showed it could eat roughly 10 percent of its body weight, which the team believed suggested makos could grow to at least 15 feet.
Chasing giants near Catalina Island
Suspecting the biggest females were hiding below, the team filled balloons with chum and suspended them at 60, 40 and 20 feet, detonating them one by one to release clouds of blood and fish remains. A mako with large teeth and beady eyes appeared but measured only about nine feet.
Another mako, the same one from the feeding test, charged the steel cage, bit it, ate some bait and retreated. A large female eventually approached but turned away after spotting the enclosure, which the team believed was because electromagnetic waves from the steel had deterred her.
The researchers then deployed a transparent Plexiglas "ghost cage," which is less visible but weaker than steel. A great white shark had ripped through a similar cage during a previous Shark Week expedition. Guttridge climbed in anyway and was lowered into the water.
He spotted a mako about 50 feet away that raced toward him and nearly struck the cage while chasing a sea lion. A second, larger mako then appeared, forcing Guttridge to leave the enclosure to get a measurement. As he moved closer, a third and even bigger female arrived and drove the other sharks away, swallowing an entire 100-pound slab of tuna.
Two makos then headed directly toward Guttridge before veering past him. Surrounded by circling dorsal fins, he retreated to the backup steel cage. The first two large sharks measured just over 11 feet and 12 feet.
As the team prepared to leave, the final enormous female emerged and seized the tuna trailing behind their boat. Guttridge could not get a precise measurement from above, leaving the shark's exact size, and the possibility of even larger makos below, unresolved.
