The shortfin mako is a strikingly blue, athletic shark with a dubious honor: its meat is considered delicious. While other species are spurned as being tough or unappealing, mako frequently shows up on restaurant menus.
Mako sharks are revered for another reason as well: they put up a tremendous fight for sport fishermen. The shortfin mako (Isurus Oxyrinchus) is the world's fastest species of shark, swimming up to 45 miles per hour. The creatures also tend to leap dramatically when hooked. “They kind of jump straight up and twirl around,” Byrne says. “There's been cases of people hooking them near the boat and then they jump and land in the boat.”
It's no wonder mako sharks are so highly regarded. But the mako shark's popularity is not doing it any favors, Byrne has found. He and his colleagues tracked satellite tagged sharks and saw that they were caught and died at rates 10 times higher than reports from fishermen suggested. This indicates that the sharks are being overfished, the team reported in August.
Other shark scientists are also finding evidence that makos in the North Atlantic are being caught at unsustainably high levels. What's more, the fast, flavorsome, but slow-growing mako may be even more vulnerable than other species to overfishing. The time has come, they say, to take action on the mako shark's plight.
“We definitely need to be concerned, and need to definitely start thinking about putting catch limits on the species which haven't existed in this part of the world before,” Byrne says.
A perfect storm
The mako shark has a few things working against it.
Mako sharks range over temperate and tropical waters around the world. In the North Atlantic, they are often in the wrong place at the wrong time. Commercial fishermen don't target makos, but the sharks tend haunt the same areas as tuna and swordfish and are caught accidentally. “They like the same water, they like the same food, and the fishermen are not trying to catch them, but they're there,” says Steven Campana, a marine biologist at the University of Iceland in Reykjavik.
Makos also reproduce slowly. “Mako sharks are particularly vulnerable even among threatened sharks because they take a long time to reach sexual maturity,” David Sims, a professor of marine ecology at the University of Southampton in England, said in an email. For females, this can take 18 years; even then, a mako will only give birth to a handful of pups once every three years.
Most of the sharks caught are juveniles that have not yet had a chance to reproduce, Byrne says. “You've got a pool of adults that are out there which we don't see very often, they're hard to catch, they're hard to find,” Byrne says. “The problem is eventually they're going to get old and eventually going to start dying…and we're going to have this vacuum where they're not going to be replaced at the same numbers.”
And then of course there's that tasty meat. “Their meat is valuable, so there's an incentive for them to not be released if they're captured alive,” Byrne says. “They're one of the few species that kind of drew the bad luck in life in that regard.”
But other sharks don't deserve such a bad rap for unappetizing meat, according to his teammate Mark Sampson, founder of Fish Finder Adventures, a charter fishing service based in Ocean City, Maryland. “Even mako shark meat, if it's mishandled, will exhibit that very strong ammonia smell,” he says. In fact, that pungent tang occurs when shark meat isn't cleaned and put on ice quickly enough and begins to warm up.
“A lot of people won't give other shark species a fair break when it comes to flavor,” Sampson says. They “think that, well if it's not a mako shark then it's not a good eating shark, which is really not true.”
Even if people were willing to chow down on other sharks, however, makos would still be in high demand. “Commercial fishermen are probably always going to welcome these sharks onboard their boat,” Sampson says.
Like other species, makos also suffer from shark finning. Sharks are often still alive when they're tossed back into the ocean after their fins are cut off, Campana says. “The new generation in some of the Asian countries is aware of this problem, and they're spurning things like the Chinese wedding soup—which is often the place where the shark fins go,” he says.
Stirrings of trouble
Initially, Byrnes and his team had been tracking mako sharks to learn more about their movements. But they were struck by how many were caught and kept by fishermen.
So the team followed 40 satellite-tagged juvenile sharks in the North Atlantic over three years. The sharks passed through the exclusive economic zones of 19 different countries. Twelve of the sharks (about 30 percent) wound up caught by fishermen from the United States, Canada, Mexico, Spain, and Cuba.
The scientists were shocked by just how many of the sharks died. “It's not uncommon for animals you tag to get nabbed by a hunter or a fishermen, but it's a really big ocean,” Byrne says. “To have that percentage of the animals that you tag…[be] harvested by fishermen, it's crazy.”
He and his colleagues calculated that each shark had a roughly 72 percent chance of surviving a year without being captured, and that the sharks were perishing at rates 10 times higher than previous estimates indicated. This suggests that makos are being fished beyond sustainable levels in this part of the Atlantic.
Earlier estimates for the sharks' mortality were based on how many makos fishermen reported catching, compiled by the International Commission for the Conservation of Atlantic Tunas (though ICCAT is focused primarily on conserving commercially fished species like tuna, the intergovernmental agency also collects data on sharks).
But not everybody reports when they catch a shark, and conventional tags sometimes fall off before a shark is captured. “I wish I knew how many of the makos that we've tagged with the other, regular types of tags were captured and nobody reported them,” Sampson says. “Apparently a lot of them are being recaptured and [the tags] are just not being turned in. Either that, or the sharks we put the satellite tags on are just the dumbest sharks in the ocean.”
The satellite transmitters, while pricier, made it easy to tell when a shark had been snared. “The shark would be out in the ocean doing shark things and then suddenly it would be transmitting from a fishing dock,” Byrne says.
They plan to repeat the study with more sharks, find some adults to tag, and track makos in different regions of the Atlantic. Meanwhile, other researchers will have to attempt similar studies to see if they find the same disturbing mortality rates, Campana says.
Even if the new estimate is spot on, makos aren't in immediate danger of extinction. But the results do indicate that their numbers are steadily dwindling. “That high a fishing mortality on makos means that the mako population is going to go down, down, down,” Campana says.
Sims says that the new findings fit with his own observations of mako sharks. “Shortfin mako sharks are less common in their oceanic habitats than they used to be,” he says. “Finding enough makos to satellite tag even in hotspots is a real challenge. There just don't seem to be many out there compared to only a decade or so ago.”
He and his colleagues have identified hotspots where mako, blue, and tiger sharks congregated across the North Atlantic, and found that 80 percent of those preferred habitats overlapped with longline fisheries. This suggested that the shark were likely being overfished in these hotspots, Sims says.
“If fishing continues at the current levels there is the chance that the shortfin mako population in the North Atlantic will reach such a low level that recovery may prove impossible even if fishing is removed,” Sims says.
As a top predator, mako sharks play an important role in maintaining the stability of ocean ecosystems. It's hard to predict what will happen if most of them are wiped out. “In cases where you lose a predator from an ecosystem, it's very rarely a good thing,” Byrne says.
Some of the fish that makos prey on could become more abundant—or another large predator might swoop in and eat even more of them. “The only thing you can predict safely is that there will be big changes,” Campana says. “It would be like wiping out the lions on the Serengeti plains of Africa, you would have huge impacts.”
About two-thirds of the ocean lies outside national jurisdictions, so mako shark fishing is unregulated over much of their range, Sims says. “There is an urgent need to introduce catch limits for shortfin mako, particularly in the North Atlantic which is fished more intensively than other oceans,” he says. “And in the longer term more large shark reserves in the open ocean will need to be considered.”
Byrne agrees that annual catch limits on mako sharks for commercial fleets could make a difference. “Those regulations don't exist for mako sharks in the Atlantic yet, but that would go a way towards helping,” he says.
Byrne and his colleagues hope that the management agency ICCAT, which has 51 nations as members, will propose restrictions on mako fishing. The annual ICCAT meetings are underway, and the organization is considering conservation measures for shortfin mako in the Atlantic, says Enric Cortés, a research fisheries biologist at the National Oceanic and Atmospheric Administration, who is another coauthor of the new paper and a member of ICCAT's Standing Committee on Research and Statistics.
Currently in the United States, a boat full of recreational anglers can keep one shark they catch per trip, provided that shark is longer than 4.5 feet from its snout to the fork in its tail. Makos don't reach maturity until they are several feet larger. However, catch and size limits for mako sharks are grouped together with blue sharks, tiger sharks, and a few other species. “Fisheries have been reluctant to have specific catch limits for each different species because a lot of anglers can't tell one…from another,” Sampson says. There are no minimum size limits on makos caught by commercial fishermen, and catch limits are looser than for sport fishermen.
If the makos do need protection, Sampson says, it might be time to increase the minimum size limit for this species. Makos do have a few distinctive features that should make them easier for anglers to identify than other sharks. “They're very blue in color, they've got a very pointed nose, they've got a very stout tail, and all that…distinguishes them from the other types of sharks that are a lot more generic in shape and color,” Sampson says.
Many sport fishermen already follow stricter size limits than the law demands. “We've always said if we're going to keep a mako it's got to be at least 100 pounds…we just estimate it,” Sampson says. Still, “There's a lot of recreational anglers who say, if it's legal it's legal, and we're going to keep it.”
If a shark that has been captured is released alive, it has a good chance of surviving, Byrne says. However, the stress of being captured does take a toll on sharks, and makos might more vulnerable than other species, Campana has found.
He and his colleagues have also tracked mako sharks with satellite tags, as well as porbeagle and blue sharks. Some of the animals that were captured by fishermen died even after being set free, and makos were especially sensitive. “Between a third and a half of them were dying either when they were on the hook struggling or afterwards when they were released,” Campana says. “That's a lot of sharks that are being killed for basically accidental reasons.” Porbeagle sharks fared similarly, but blue sharks were a little more resilient, he says.
Being snagged and released can be a harrowing experience. “They're thrashing around in the water, they're building up stress hormones,” Campana says. “In high enough levels these make any animal more susceptible to death.”
As fast, active sharks, makos and porbeagles need a lot of oxygen, he says. But when they are on the hook, their range of movement is limited. “They simply can't swim to ram the water and the oxygen over their gills fast enough,” Campana says. “Some of them are dying form lack of oxygen before they get pulled up on the boat.”
Another problem is that not all fishermen will release a shark by snipping the fishing line or using a dehooking tool. “It can be fairly brutal, it could involve the fisherman cutting the jaw open to retrieve the hook or trying to rip it out of its mouth,” Campana says.
If a shark survives the first day or two after it is released, it has a good chance of weathering its injuries and stress, Campana says. But his findings indicate that releasing sharks does not guarantee that they will live. “Certainly catch and release fisheries are good,” Campana says. “But it is a mistake to assume that they're all going to survive.”
That means that fisheries managers will also have to consider this delayed mortality rate in their calculations. However, there are a few things that sport fishermen can do to make sure that being hooked is minimally traumatic for the sharks.
“It's mostly just using commonsense practices from the time they hook the fish until they get it to the boat,” Sampson says. “Try to catch the shark in a timely manner, and when you get it to the boat be prepared for it.” That means everyone should have their cameras ready and know where they will stand in a photo, and someone should have wire cutters or a dehooking tool handy so the shark can be released as quickly as possible.
Fishermen can also stick to circle hooks, which are designed to hook in the corner of a fish's mouth rather than down in the gut. Eventually, the hook will rust and fall out. Starting in 2018, recreational shark anglers will be required to use circle hooks in most circumstances. The new regulations will give makos and other sharks a better chance of survival after release, Sampson says.
Make way for makos
The shortfin mako is considered a vulnerable species worldwide, and researchers are finding more and more signs that the ones dwelling in the North Atlantic are in trouble.
Campana says that he was not surprised to hear Byrne and his colleagues report that the mako's mortality rate is higher than previous estimates suggested. “I and many other shark biologists have long been worried that the official statistics for mako—how many are caught etcetera—are just grossly, grossly wrong,” Campana says. “It's a great wakeup up call for what's going on. Because if the mako are being that underreported almost certainly the other big sharks are as well.”
But there is hope; sharks can bounce back from human meddling. Great white sharks were nearly decimated in the Atlantic between the 1970s and 1980s. Since they became a federally protected species in 1997, the sharks have made a comeback, and the population has grown to 70 percent of what it was in 1961.
Putting limits on the size or number of makos that can be kept by fishermen could help the sharks rebound. But in the meantime, Sampson says, sport fishermen can help by bringing fewer of the makos they catch home for dinner. “Even though mako sharks are food fish, anglers shouldn't think that it's okay to harvest them with the same frequency that they do the other food fish,” Sampson says. “There's lots and lots of tuna and mahi-mahi in the ocean, but there's only a few sharks.”
Mako sharks have long been valued for their fighting prowess and tasty meat. Now, Sampson says, “It would really be great if more recreational anglers would adopt the respect and the admiration of makos to the point where they would just enjoy the opportunity to catch one, interact with them and turn them loose.”