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 first worked with number tags to get a sense of the shark population, and Aming explains their limitations. “You might put ten tags out, and only get one or two back,” he says, as the more basic tags rely on a tagged shark firstly being caught, and secondly, the fisherman informing you that it was caught. Even then, you only get two data points; where it was tagged, and where it was caught – not enough for an in-depth analysis of a shark’s movements.
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.
Aming explains the two types of tags that they use – bolt-on and tow tags. Bolt-on tags bolt to the fin and transmit a satellite ping every time the shark surfaces, which draws you a map of shark movements. The tow tag measures depth and temperature, as well as light levels. Using the light levels, the tag estimates where the shark is on the earth. While less accurate for location data, it means that the shark does not have to surface to paint a picture of its movements.
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.
Besides the pure data from shark tags, Aming has also learned a lot from simply observing the sharks and getting video recordings of their behaviour. He has observed what can only be called a feeding hierarchy, although he has not been able to ascertain its structure, or the shark’s motivations. Observing which tiger shark goes for the chum the team puts out first, Aming says “it’s not necessarily the biggest one; it could a smaller one who’s acting more aggressively.” Though the pattern is unclear, Aming says, “they definitely take turns.”
Such caution may not be expected from a creature that the world has labeled a brainless predator, sometimes referred to as an ‘eating machine.’ Aming notes that “they are slow, methodical, and they test. If we put a 150 pound chunk of marlin out for them to eat, they might swim up to it, bump it, smell it, feel it with their head. I’ve never seen a wild tiger shark just cruise in and attack something.”
This is certainly consoling information for those who are worried about shark attacks in Bermuda. As Aming puts it, “you wouldn’t survive if you ran in just biting everything. One day you wouldn’t be successful.” For tiger sharks to survive, they must examine unfamiliar items to discern if they are worth making in to prey, and humans are something they have rarely encountered before.
There is a record of shark encounters in Bermuda, which Aming has looked through and evaluated. He believes that only one on the list is a “legitimate shark attack” – an unprovoked attack where the individual was inshore. “May 24th 1960, someone got bitten by a tiger shark. They survived, with stitches. It was a waiter, who was just swimming. He got hit from behind and probably thought it was his friends.” Aming explains that the shark was probably bumping him, their most common tactic for investigating new things they find in the ocean.
Aming postulates that the man’s hand probably got caught on the shark’s mouth, causing the damage – he says that if it were a true attack, “the damage would have been a lot more.” In a tragic ending typical of public opinion of sharks at the time, authorities put a boat in the water off elbow beach, and caught a shark they suspected to be the culprit. They brought the animal on shore and beat it to death with oars in a grisly and twisted retribution.
The Bermuda Shark Project’s observational research provides evidence of the shark’s curious, rather than bloodthirsty behaviour around humans. Aming recalls a spectacular encounter with a female tiger shark, which rarely visit Bermuda. “The first adult female we ever had was very relaxed. I’d love to find another to see if that is the norm. We could swim around with her, ride on her fin, and play with her.”
The Shark Project didn’t start out as a research project at all, but simply a group of people who were interested in interacting with sharks. The late Dr. Neil Burnie, along with Jeffrey Manson and Tim Hasselbring, were working on making a shark cage, and when they learned about Aming’s videography experience with whales, they knew he had to come along to capture the event if anything exciting happened. Aming had been diving around Bermuda, but had never seen a shark, and as soon as he saw them off shore, he was spellbound by their size and power. “I said, that’s it, I’m hooked,” as he recalls his first time seeing sharks. Though the thrill of being close to sharks was remarkable, each team member also had a deep respect for the oceanic giants, which only increased as their research yielded more results.
Many gaps still exist in the knowledge we have about tiger sharks. For example, we don’t know exactly what they are eating when they are in Bermuda. Scientists like Aming can only get a good idea of diet through performing a necropsy, and the only way they would get to look inside the stomach is if they found a shark already dead. “I saw one cough up a longtail once,” Aming said, “that was interesting to see.”
In addition, the breeding habits of tiger sharks are largely unknown. “We’re pretty sure the breeding happens in the Bahamas,” Aming says, but notes that there have been newborns caught off Bermuda, so young that they still have umbilical scarring.
One thing we do know is that there should be many more sharks present than we are seeing inshore currently. Aming explains, “people ask me if I’m worried about the hammerhead. The question they should be asking is ‘why is there only one?’ The sign of a healthy ecosystem would be to have a lot of predators.” Sharks have been the victim of overfishing for decades in Bermuda, and there are still no local laws to protect them, though many shark species are endangered.
Aming clarifies that the thought that the reef line keeps out the large predators is a myth. “You get the megaship in twice a week – anything can swim in,” he remarks. He notes that many people hold the belief that Bermuda is protected from sharks inshore because of our reef line, but the real reason we see so few sharks inshore is their alarmingly low numbers. And when you have low numbers of predators, it’s a good indication that the ecosystem is not healthy.
Aming explains that there are dangers in letting populations of species that sharks would prey on become unchecked. “We don’t know what the ramifications are,” he says, “you want to leave nature’s balance as natural as possible.” Because ecosystems are so interwoven, you never know what cascading effects may come from obliterating a single species. The land crab is an example of a terrestrial species that became superabundant after the extinction of their predator, with consequences for the rest of the ecosystem, and you can read the story in detail here.
Besides regulation on an ecosystem level, predators also act to stamp out disease in the populations they prey upon. Since they are easier to catch, sharks target weak or diseased fish, and this has the effect of keeping the population healthy. If no predators pick off the weaker individuals, you could even get a situation where a disease takes over, and wipes out an entire prey species.
Aming notes that overfishing is the number one threat to sharks in Bermuda. “One thing I don’t like locally is typically people see a marine creature, and think ‘I should eat it!’ We could leave a few things in the sea.” Because our platform is so small, it takes very little time for it to become overfished, and a long time for it to recover while fishing still continues. However, Aming notes that populations do bounce back when fishing restrictions are applied, and that Bermuda is in desperate need of a no-take zone.
“They’re not even that good of eating,” he says. “They’re full of uric acid. If you kill a shark and leave it, the acid decomposes to ammonia. That tangy taste you’re tasting? That’s ammonia, that’s what the ‘bite’ is.”
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.
Ultimately, the amount that we don’t know about sharks tremendously outweighs what we do. The importance of their research and conservation has only been realized recently, and as a result we have no idea how numerous sharks once were. Aming is still tagging more sharks, and hopes to glean information about shark life cycles by tagging juvenile specimens. Though there are no local restrictions in place, he wishes that sharks are left alone, and get the chance to thrive again.
Take a look at the Guy Harvey Research Institute’s website to view the data collected by the Bermuda Shark Project’s shark tracks.