Fae Sapsford speaks to Choy Aming, an associate of the Bermuda Shark Project, to discuss shark populations in Bermuda. For full article, see The Bermudian.
Sharks are undoubtedly one of the ocean’s most well known predators. Humans are always startled by the few threats in the natural world that we have not overcome, and which still pose a danger to us, and as such, the interest and alarm over sharks is huge. Despite this fact, sharks are some of the least studied animals in the world for all of their fanfare.
Many challenges come into play when trying to research the pelagic predators, and I sat down with Choy Aming, an associate of the Bermuda Shark Project, to talk about them. The primary hurdle in studying the oceanic predators may be the difficulty in actually capturing them for study. Ornithologists can use a net that birds fly in to and get caught in, and handle the specimens with ease; but shark scientists have to go to the sharks, facing the difficulties of working on the ocean, and the strength of an eight hundred pound predator.
Aming notes that while they obviously want to return the shark to the water in the best condition as possible after tagging them, it is advantageous to the researchers when the sharks are tired out. “They need to have been a little winded,” he laughs, recalling times when the team managed to get a shark subdued too quickly, and had to wrestle with attaching a tag to its fin. “If you don’t fight with them for an hour before subduing them, they’re incredibly strong.”
The best way to obtain sharks for research is by fishing them out. The team uses circle hooks with the barbs filed off in order to cause the least damage to the shark. The hook rolls in to the corner of its mouth, and at this point, the researchers can strap it to the side of the boat in order to attach a tag. Sharks under 150 pounds can be brought on deck, and have water run over their gills with a hose until the scientists are ready to release them. However, most of the sharks they see are ten to eleven feet long, weighing hundreds of pounds. [. . .]
The team observed sharks at Challenger Banks in deep water, and noticed that they were usually present in the warmer months. They tested out their shark wrangling skills by putting inexpensive number tags on various tiger sharks, and they were able to observe the same individuals returning to the Challenger Banks area. By going back about two times a week in the early stages of the project, and seeing the same shark in the area, they got their first data points.
“Satellite tags have changed the game,” Aming explains, because free roaming pelagic species, like sharks, can now be tracked more accurately and comprehensively, allowing the collection of information robust enough for research. Some tags still rely on the animal surfacing to transmit data, which is perfect for often-surfacing animals such as turtles and whales, but on a shark would mean that much of its travel path would be lost. [. . .]
Satellite tag technology had made it easier than ever to study sharks, but at six or seven thousand dollars per tag, expense was another barrier to shark research. Aming explains that a tagging mission could cost hundreds of dollars – for fuel, equipment, and bait, not to mention the tags themselves. However, with support from BAMZ, and the Guy Harvey Research Institute, and local businesses, the project has been able to shed light for the first time on the mysterious life of the denigrated fish.
What they found was astonishing. They quickly realized that almost all the tiger sharks in Bermuda are migrants, coming originally from the Caribbean. After tracking shark movements for a few years, they noticed a distinct pattern that could only be described as a migration. Aming explains that they spend time hunting on the northern ridge of Caribbean island during the winter, and in late spring and early summer they come up to Bermuda. “It seems they follow an eighty degree temperature gradient,” he says. “They do it not only in the same pattern, but on the same time scale.” He recalls that one of the tagged sharks, Harry Lindo (sponsored by the grocery store), would leave within the same week every year and return within the same week every year. “They can time getting back home almost to the day,” Aming remarks amazedly.
It is clear that tiger sharks have an acute sense of navigation, which calls for further study. Just as turtles can happily navigate the vast oceans and return to their same nesting beach, it appears that sharks know exactly where they are in the Atlantic at any given time, and that their movements are deliberate. Aming wonders how the ability has evolved in to them, remarking that sharks are some of the oldest creatures in the sea, going back 200 million years. “I think the only thing that beats them is maybe jellyfish.”
It makes sense that tiger sharks like warmer water, because one of their main food sources are turtles, and turtles favour warmer water too. Aming even notes that one of their turtle tracks lined up almost exactly with one of their shark tracks, showing strong evidence that part of the reason for shark migration may be because of prey distribution. [. . .]
One of the only shark populations in Bermuda that hasn’t been affected by overfishing is that of the sixgill shark. “We had to put two thousand feet of steel cable to get one to come up,” Aming says, as the sharks live so deep in the ocean. He was astonished by how many they caught in a short space of time, and postulates that they would have been unaffected by overfishing because they would never come in to contact with fishermen. “Their population could be identical today to the population here four hundred years ago, before people got here.”
Tiger sharks, on the other hand, used to be much more numerous in Bermuda, but the lack of interest in researching them means that we have no baseline population numbers for them. Aming explains that, in the absence of concrete historical data, he has resorted to talking to fishermen about their experiences with sharks. “A lot of people have stories of catching them closer to shore,” Aming says. He recalls one story a fisherman told him, who caught a shark off of Saltus Island. He was in a twelve foot punt, and caught a shark longer than his punt, which gives Aming a reliable piece of data. The fisherman hauled it back to Spanish Point and put it on a crane, charging people a shilling to look at it, which tells Aming a shark of that size was seen before 1968, which is when the Bermuda dollar was introduced. [. . .]