Male tiger sharks undertake incredible journeys as they patrol the waters of the mid-Atlantic, researchers reveal. They’ve discovered that the creatures swim thousands of kilometers each year as they migrate between the Caribbean's coral reefs and the waters of the mid-North Atlantic. This is the longest amount of time scientists have managed to track tiger sharks, and the results show that the feisty fish behave much more like turtles and whales than anyone previously expected.
“These repeated journeys were very unexpected,” said James Lea, who led the study published in Scientific Reports. “The tiger shark has traditionally been considered a coastal species, and it is rare among sharks to so easily and habitually switch between the two vastly different environments.”
Most large shark species are tricky to tag and track for more than a few months, mainly due to logistical limitations. But the researchers from Nova Southeastern University were able to follow a total of 24 sharks, some for over three years. They showed that the sharks traveled huge distances, averaging over 860 kilometers (534 miles) a month, and making round trips of more than 7,500 kilometers (4,660 miles) as they migrated between the warmer waters.
A tiger shark doing a really good job at showing how they get their name. Credit: Nick Filmalter/Danah Divers
Quite incredibly, Harry Lindo—one of the sharks—was tracked as he traveled more than 44,000 kilometers (27,300 miles) across the ocean, putting him in the record books. He’s possibly the furthest tracked tiger shark ever, and potentially the longest tracked distance for any shark. “It is truly remarkable,” said Guy Harvey, one of the researchers, of the creature's travels. Amazingly, the sharks even return to the same islands in the Caribbean each year.
Now that they’ve found out that the sharks make these mammoth journeys, they want to figure why they do it. “There's got to be something really good up there to make the sharks undertake such massive, repeated swims, but exactly what is a puzzle,” said Mahmood Shivji, another member of the team.
They know that female tiger sharks often hang out in the Caribbean during winter, so this might explain what draws the guys there during this season, but what is less obvious is why they then move further north in the summer. One theory is that they follow juvenile loggerhead turtles who also move north at this time, as the sharks have been found with the remains of the turtles in their stomach. But at the same time, there are plenty of other turtle species that don’t migrate north, so that might not be the whole picture.
“Understanding how these animals use the oceans is the first step toward effective conservation,” explained Harvey. “Protecting migratory species is a great challenge because they can be found in such a wide area. Protecting the areas where animals, such as tiger sharks, spend the most time is a tractable goal once those areas have been identified.”