Mako shark populations to take half century to recover from overfishing

            An essay in this month’s newsletter of the Rhode Island Saltwater Angler’s Association claims that populations of shortfin mako sharks – a popular sportfish and a tasty offering on local menus – are “in crisis,” with fewer and smaller mako sharks being caught compared to 25 years ago. Written by Long Island attorney Charles Witek, a recreational fisherman who identifies himself as a consultant on fisheries management issues, the essay also criticizes the measures adopted to reduce shark mortality and the long timeline for rebuilding the population.

            “Even if such reductions could be achieved, it will take about 50 years to return the shortfin mako stock to something resembling a healthy level of abundance,” Witek wrote. “Which, in turn, means that I and probably most of the people reading this article, will never see a healthy mako population in our lifetimes.”

            Although shark biologists in southern New England disagree that makos are in crisis,

Short-fin mako shark (Stock)

those surveyed agree that the species is being overfished and that, even if targeted fishing for the species around the world was eliminated entirely, it would likely take at least several decades for the species to recover to healthy levels.

            “In the world of fish, mako sharks are like a Lamborghini or a Corvette or a Ferrari,” said Greg Skomal, a shark researcher and senior scientist at the Massachusetts Division of Marine Fisheries. “It’s a high-performance fish from a physiological point of view. Its body is built for speed, it’s really well adapted to its environment, and it’s a very efficient predator.

            “Those same attributes make it fun to catch for recreational fishermen because they leap out of the water and they’re strong fighters,” he added.

            Last year, the International Commission for the Conservation of Atlantic Tunas, the agency that manages mako sharks in the North Atlantic, concluded that the sharks are being overfished – too many are being killed by commercial and recreational fishermen to sustain the population. The commission recommended two management strategies designed to rebuild the population: Commercial long-line fisheries, few of which target mako sharks, should release any mako that is still alive; and the minimum size limit of sharks captured by recreational fishermen should be increased to 83 inches, which is about the size when they become sexually mature.

            “That translates into fewer dead mako sharks, higher survivorship, and rebuilding of the population,” said Brad Wetherbee, a University of Rhode Island professor who studies mako sharks. “But they realized that it could take until 2070 for mako sharks to rebuild and reach sustainable levels. It’s a slow process.”

It’s a slow process because mako sharks grow slowly, they take a long time to become sexually mature, and they give birth to relatively few young.

            According to Skomal, the United States accounts for only about 10 percent of the landings of mako sharks in the North Atlantic. Most are caught as bycatch by commercial longline fishermen targeting tuna and swordfish. Spain and Portugal have large longline fleets that target mako sharks in the mid-Atlantic, and many other nations primarily catch them as bycatch.

            “We’re small players in the mako market,” he said. “The argument I hear from recreational and commercial fishermen in the U.S. is that we’ve already done a lot for the conservation of makos, and other countries need to step up. But the conservation community says, no, everyone has to pull their weight, which means the U.S. has to reduce its landings further. Some conservation groups are calling for a complete moratorium on mako fishing.”

            That’s not likely to happen, since more than 50 nations fish for mako sharks. And even if targeted fishing for the species is eliminated, mako sharks are still going to be killed unintentionally.

            “If the Portuguese landline fleet targeted only blue sharks, they’re still going to keep catching makos and bring them in if they’re dead,” he said. “There is never hypothetically zero mortality, unless you pull the fleets off the water and reduce fishing effort, and that’s not going to happen. There will always be bycatch mortality, release mortality and illegal mortality.”

            So how did the mako shark population get in such a dire situation in the first place? Skomal said it started with poor historical recordkeeping about shark landings from shark fishing nations, including the United States.

            “We can’t identify a problem if we don’t have good data on which to build a good assessment,” he said. “In the case of sharks, most historical data sets don’t differentiate by species, so it’s difficult to look at historic trends. We also don’t have good reporting from all nations, which means we end up with flawed data. If big fishing nations don’t fully report, then you don’t fully account for all of the mortality.

            “Now that we finally have good data, we suddenly see that we’ve been hitting this species too hard,” Skomal said.

            Wetherbee has been tracking the movements of mako sharks since 2004, and more than 25 percent of the sharks he has affixed with satellite transmitters have been caught and killed by commercial or recreational fishermen. His data, which showed that the mortality rate of mako sharks is more than 10 times higher than the rate previously estimated, contributed to the assessment that the sharks are being overfished.

            “They grow over 10 feet long and over 1,000 pounds, but people hardly ever see makos that big now because there aren’t that many big ones out there anymore,” he said.

            After more than 15 years of studying mako shark movement and migration patterns, their habitat use, fishing mortality and other topics, Wetherbee is pleased that his data is being used to inform policymaking. But he’s not sure the recent policy recommendations go far enough.

            “I have a more radical opinion than most people,” he said. “I don’t think they should catch and kill them at all. But most people aren’t going to subscribe to that. If they were being fished sustainably, I’d say go ahead and catch and eat them.

            “We’ll see if the actions they’ve taken to rebuild the stocks are going to be effective,” Wetherbee added. “It’s a step in the right direction. They could have done more, but they didn’t.”

This article first appeared on EcoRI.org on January 26, 2020.