Sharks inspire a range of emotions in humans. We shiver at the sight of a fin in the water, but millions of people also tune in to “Shark Week” every year on the Discovery Channel to learn all about them.
As much as humans might fear them, many sharks are actually in danger of disappearing altogether. According to a press release from the University of California Santa Barbara, nearly two thirds of sharks globally are in danger of extinction – mostly as a result of fishing. Research published this month in the Fish & Fisheries journal identified something that might help, but it might not be enough.
“Our study shows that retention bans could reduce shark mortality, but must be combined with additional measures to stop overfishing, especially for low-productivity species,” said the study authors.
Examples of retention bans include a prohibition of commercial recreational retention of oceanic whitetip sharks in all U.S. waters of the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea and Hammerhead sharks in the U.S. Caribbean announced last January by the National Oceanic and Atmospheric Administration. Both types of sharks are listed as threatened under the Endangered Species Act, said the NOAA.
Currently, 17 oceanic shark species are covered by retention bans to protect them from incidental catch in tuna fisheries. However, the researchers explained why these efforts have limited results.
“More than half of sharks that are caught and killed in fisheries are captured incidentally and then discarded,” said Darcy Bradley, co-author of the study and adjunct faculty at the Bren School of Environmental Science & Management and lead scientist at The Nature Conservancy.
Allie Caughman, co-lead author and a doctoral candidate at the Bren School, said that the team wanted to find out how many sharks incidentally captured by fisheries were already dead by the time they are landed or die shortly after release. The team was also curious how certain regulations affected shark survival.
They collated available data from more than 150 published papers and reports that have measured shark mortality to address these questions. Close to 150 shark species were covered in the reports.
“Using this information, they could estimate mortality rates for an additional 341 shark species incidentally captured by longlines or gillnets but for which empirical data wasn’t available,” said the press release.
Among the sharks facing the greatest threats are smaller sharks, which are more likely to die after being caught, and deep-water sharks. Thresher sharks and hammerhead sharks were also some of the most threatened species.
While policy simulations demonstrated that retention bans could actually reduce shark mortality three-fold, those simulations also showed that even that much of reduction wouldn’t reduce “mortality to sustainable fishing levels for already heavily fished species, like mako and silky sharks.”
In particular, the researchers said the bans are most likely to benefit species with faster reproductive rates, since those populations recover faster. Blue sharks, bonnetheads and angel sharks are in this category.
“While it is highly unlikely that retention bans will ever be implemented for such a commercially important species,” said Leonardo Feitosa, also a doctoral candidate at the Bren School, “our results show that this could be a relatively simple and impactful strategy if it becomes necessary to sustain populations.”
For other sharks, additional strategies will be needed to sustain healthy populations. These could include area-based fishing restrictions, catch quotas and fishing gear requirements such as banning the use of steel wire on longlines. Going forward, the researchers said that more data on mortality rates for other cartilaginous fishes, such as stingrays, skates and chimaeras.
“Fifty-seven percent of cartilaginous fishes threatened with extinction in the world are not sharks,” Caughman explained.
One bright spot in the outlook for sharks is a “remarkable comeback” on the East Coast of the U.S. that Audacy reported on last summer. Even as efforts to sustain shark populations continue, people are still advised to be cautious around them, since they do indeed bite sometimes.