NAUSET BEACH, Mass. — It was an aquatic case of serendipity.
Nearly three years after a female basking shark was tagged with a satellite transmitter at Malin Head, the northernmost point of Ireland, she happened to be photographed at Nauset Beach, Massachusetts.
The event marks the second-ever recorded observation of trans-Atlantic movement of the species, according to a study from Queen’s University Belfast and Western University in Ontario, published in the Journal of Fish Biology in October.
On its face, this may not seem like a remarkable event, but the number of unlikely occurrences that perfectly aligned to make this shark’s identification possible would make even the most ardent skeptic wonder whether it was an intercedence of fate.
And even more fortuitous is the fact that this resighting provides a window into the movement of one of the ocean’s most bizarre-looking fish, which has a huge, striated structure in its mouth where one might expect smooth flesh to be.
A three-year tale
The series of fortunate events started in August 2014, when the shark was tagged with a satellite transmitter just off of Malin Head, a hotspot for basking sharks in the northeast Atlantic. After a few months, the device stopped transmitting data.
“That’s not unusual,” said Jonathan Houghton, one of the study’s lead researchers at Queen’s University Belfast. “If you put electronics in the sea, some things just glitch up after a while.”
But then, out of the blue in June 2017, the shark was photographed by an underwater photographer more than 4,600 kilometers away, off the East Coast of North America.
The photograph made the rounds in Europe, and when it reached the research teams, they noticed something astonishing: Attached to the shark’s no-longer-functioning tracking device was a small, unmistakable gadget that the researchers had fashioned themselves as a buoyancy aid. At the time, this shark was the only one that was wearing the modified device. They realized that this was the same shark they had tagged nearly three years prior.
This marked the second time this species had been observed to move across the Atlantic, the first being in 2008.
“Until that moment, we had never been able to follow the movement of a shark for more than, say, nine months or a year. So to understand its movements on a time scale of three years, on a different side of the Atlantic, that’s completely changed the way we think,” said Houghton.
And it wouldn’t have been possible without a stroke of luck. “Scientists love to say that everything we do is based on absolutely brilliant pre-thought. But sometimes, we just get lucky,” he admitted.
Shark of interest
The basking shark has long been a species of interest. The public has shown interest because of its unusual (to put it mildly) appearance. Scientists are more interested in its dwindling Pacific population.
“In the mid-20th century there was a lot of conflict between basking sharks and commercial fisheries,” said Paul Mensink, who conducted the research at Western.
Measuring in at up to 12 meters (40 feet) long, it is the second-largest fish, and it has a habit of colliding with boats and getting entangled in fishing equipment. This led to a targeted effort to eradicate the sharks in the Pacific. “There’s a bit of a dark history on the Pacific coast,” Mensink said.
In the Atlantic, however, the species is healthier. Here, the sharks have two populations, one in the northeast Atlantic near Ireland and Scotland, the other in the North American region of the ocean.
The journey of the shark from the northeast Atlantic to North American waters represents a mingling of these two populations. “We knew that trans-Atlantic movement could happen but it wasn’t very common,” said Houghton.
What they didn’t know prior to this study, however, was whether sharks that ventured across the Atlantic tended to return to their native populations. “That this animal, three years later, appeared to have become a part of the North American population is a very new finding,” said Houghton. “There’s not a kind of bungee cord effect where they have to return back to the other side.”
When you think about it like that, said Mensink, “the oceans get a little bit smaller in a way.”
What’s in its mouth?
It likely wasn’t only Houghton and Mensink who did double-takes upon seeing the photo. Most people who stumbled across it were probably tempted to stare. To the untrained eye, the inside of the basking shark’s mouth appears to contain a ribcage.
That’s, of course, not what it is, as sharks are cartilaginous fish that lack bones, explained Houghton. It’s actually tough, structured cartilage that’s only visible when the shark’s mouth is open.
The structure may not be a rib cage, but it serves some of the same purposes. “When the shark opens its mouth, it’s kind of like opening your jacket on a windy day. It inflates out and that cartilage gives it some structure so that its skin isn’t just flapping around,” said Houghton.
It also serves the less practical purpose of making the basking shark one of the most bizarre-looking fish in the ocean.