Fishing Strategy Mitigates Shark Attacks
The combination of recreational beach use and disruption of coastal ecosystems has led to an increase in shark attacks on humans in some areas. Many countries, including South Africa and Australia, have implemented shark control methods to prevent these attacks. One of the most common methods is called “shark meshing.” Shark meshing involves capturing sharks offshore with traditional mesh gill-nets. Once captured, the sharks are either killed or released in deeper ocean waters where they are less likely to attack humans.
While live release of sharks is the goal, some die in the gill-nets before they can be released. Additionally, other large-bodied sea life accidentally gets caught in the nets during fishing. These species, called “bycatch,” usually perish despite posing little or no threat to humans. Common bycatch includes dolphins, manatees, sea turtles, and ocean catfish.
A study conducted in Recife, Pernambuco, Brazil, revealed a better solution to shark management. The Recife region saw 55 shark attacks on humans along one 20-kilometer stretch of coastline between 1992 and 2011. Prior to 1992, no attacks were recorded even though the area has served as a popular recreation area since the 1950s. This sudden outbreak made people less likely to visit the beach, thereby hurting the local economy. In response, Recife government commissioned a project called the Shark Monitoring Project of Recife (SMPR) to keep people safe from sharks, protect sea life, and learn more about the ocean ecosystem in the waters off Recife.
The SMPR used a combination of longlines and drumlines to capture sharks on baited hooks before they reached the Recife shoreline area. Longlines were four kilometers long, anchored to the ocean floor by five moorings, and were fitted with 100 hooks each. Drumlines are vertical fishing lines suspended by a buoy and anchored at the bottom to maintain tension. The drumlines were each outfitted with four hooks.
Two longlines were set out during the fishing expeditions to blockade the sharks. One was placed at the north end and another at the south end of the Recife shoreline. SMPR also placed drumlines alongside the longlines. In 8 monthly fishing expeditions, the lines were hauled in within 24 hours to reduce the time that animals were trapped on the hooks underwater. Once the fishing lines were brought aboard the fishing boats, non-aggressive bycatch species were identified and immediately released. Potentially aggressive shark species were identified, tagged, and released in deeper waters further from the Recife shore.
This fishing program ran for 73 months between 2004 and 2011. There were 11 shark attacks during this time, but 10 of these occurred during a 23-month period when funding gaps put the project on hiatus. Thus, only 1 shark attack occurred when the fishing program was active. Of the captured animals, 7% were potentially aggressive shark species, the mortality rate for which was 30%. The mortality rate for bycatch species was 22%. The SMPR fishing project caught a handful of species protected under Brazilian law, such as the goliath grouper, but none of these species perished. No mammals were caught by the SMPR, meaning that the longline fishing method was better at targeting sharks than shark meshing.
Despite its success, the SMPR program has some drawbacks. First, while the program successfully protected humans from sharks in Recife, similar programs in Hawai’i didn’t reduce the shark attack rate. This means that physical coastline features and differences between shark population may account for SMPR’s success. There was also a reported increase in shark attacks north of Recife after 2004, which might mean that sharks captured and removed from Recife simply migrated to other coastal areas. Second, SMPR’s shark capture method targeted both dangerous and harmless shark species. While mortality rates for most of these species was low, the harmless blacknose shark suffered an 80% mortality rate during the project.
Overall, SMPR’s method, though far from perfect, is still preferable to alternative methods that are even less discriminate. This study indicates that longline fishing may be a significant improvement over shark meshing as a strategy to protect both sharks and human beachgoers.