National Geographic : 2017 Aug
132 national geographic • aUgUSt 2017 fishermen on board reeled in two small makos, neither of which put up much of a fight. So I de- cided to try again—this time with a seasickness patch—in Rhode Island later in the summer. And that’s when I saw what I really needed to see. On each trip I accompanied scientists affil- iated with the Guy Harvey Research Institute, which has been tagging and tracking makos in the Atlantic Ocean and Gulf of Mexico since 2008, with the primary objective of studying the sharks’ movement patterns. Makos in the west- ern North Atlantic are highly migratory, traveling northward during the warmer months and then south as winter approaches. The excursions off Maryland’s coast in May were a resounding suc- cess: Over two weeks, 12 makos were fitted with satellite transmitters. By contrast, the Rhode Island excursions in August were a resounding failure: one week, zero makos. But that contrast offered a clue as to what might be happening with makos in the Atlantic. To pick up on the clue, you have to know one of the first things you learn when you’re fishing for makos: They share territory with blue sharks. The two species are kind of like lions and hyenas, co- existing in the same areas as they pursue different feeding strategies. Shortfin makos are the fastest sharks in the ocean, capable of reaching 35 miles an hour as they chase down speedy prey such as bluefish and tuna, and sport fishermen love their power. Blue sharks, on the other hand, are rela- tively laconic and focus on slower prey, like squid. Catching them is like, in one fisherman’s words, “reeling in a barn door,” and their meat is not nearly as good to eat as a mako’s. So you can guess which one is the lion in the analogy and which is the hyena. Everyone wants to bag the lion. On our second day out of Narragansett, Rhode Island, as we hauled yet another blue shark to the side of the boat, I finally took note of the obvious. “It seems like all the blue sharks have hooks in their mouths,” I said. Brad Wetherbee, the marine ecologist from the University of Rhode Island who was there to tag any makos we caught, said, “Yup. Every one we’ve brought back to the boat so far has had a hook in it.” Removing a hook from a shark’s mouth can be dangerous, so fishermen just cut the leaders and leave the hooks to rust away. And because the fishermen are after makos, they’re much more likely to release blue sharks. “I’ve never seen a mako with a hook,” the ship’s mate, Lucas Berg, told me our first day out. “People don’t ever let them go. But we’ve caught blue sharks with four hooks in their mouth.” The fishing pressures on makos are intense, Wetherbee explained. The ones we were trying to catch swim northward up the Atlantic coast in the summer, and between everyday recreational fishing and the dozens of shark-fishing tourna- ments held between Maryland and Rhode Island, it’s a perilous journey for the sharks. “A lot of them have been weeded out by the time they get up here,” Wetherbee said. “Is the catch rate sustainable?” I asked him. Ma- kos, like many sharks, are especially vulnerable to overfishing because of their small litters and high age of sexual maturity. (One study suggests that female makos don’t reach maturity until around 15 years old or later, but these figures are not de- finitive. Biologists agree more research is needed.) “ We don’t know,” he said. “ These are far-ranging, international sharks—some of our [tagged] makos have gone into the waters of at least 17 different countries—and there’s not enough data for man- agement agencies to come up with a good estimate of whether the population is going up or down or staying the same. There’s probably some number of mako sharks that would be fine to catch and kill. But we don’t know if it’s 100, or 1,000, or 100,000.” According to the National Marine Fisheries Ser- vice, which regulates fishing in U.S. waters, makos are being fished at a sustainable level. This assess- ment is based largely on catch figures supplied by commercial long-liners to the international orga- nization that regulates fishing for tuna and other pelagic fish in the Atlantic, and those figures show a relatively consistent harvest over recent years, suggesting that mako populations are stable. But the figures are an imprecise measure. The catch is recorded in metric tons, and basic information n Society Grant Your National Geographic Society membership helped fund this project.