Many species were found to be missing from reefs they once occupied in large numbers, making them “functionally extinct.”
Written by Zachary Huang-Ogata
For the past decades, shark populations around the world have been devastated by a myriad of threats, particularly due to overfishing, but a new study reveals that the absence of these sharks is even more widespread than previously thought.
The groundbreaking study, published in Nature as part of the Global FinPrint survey, found that across 371 coral reefs in 58 different countries, sharks were completely absent from one in every five reefs. Many species including the grey reef, blacktip reef and Caribbean reef shark were found to be missing from reefs they once occupied in large numbers, making them “functionally extinct” and unable to fulfill their normal ecological role.
“We expect, as a condition without humans, that there should be sharks on every reef in the world," says Aaron MacNeil, the lead author of the study. "To find 20 percent of the reefs that we surveyed didn't have sharks is very concerning."
Sharks are known as apex predators, meaning that they carry an incredibly important role in maintaining the delicate balance, abundance and biodiversity of marine species. As stewards of reef systems, shark sightings in these areas serve as key indicators of ocean health and a thriving ecosystem.
Even though sharks remain at the top of the food pyramid, they are by no means invincible. Sharks are a “K-selected” species, which means that their slowed growth, delayed maturity and limited production of offspring makes them especially vulnerable to catastrophic population declines.
“Worldwide fisheries are already collapsing, even the big ones with tuna and lobster, both of which have high reproductive rates and are fast-growing organisms,” says Gerardo Peña with environmental NGO Ninth Wave. “Now imagine a reef shark, which takes 4-8 years to reach sexual maturity, having only 2-6 offspring at a time. The basic biology of the shark already puts it at a disadvantage.”
Researchers also determined that losses in shark populations were due in large part to unregulated and destructive fishing practices, such as overfishing, finning and the use of longlines and gillents.
"Although our study shows substantial negative human impacts on reef shark populations, it's clear the central problem exists in the intersection between high human population densities, destructive fishing practices and poor governance," says Demian Chapman, co-lead of the study and associate professor at Florida International University.
By banning harmful fishing practices and enacting protective measures like shark sanctuaries, experts are hopeful that populations will be able to rebound over the next coming years.
But they also emphasized that saving the sharks would require scientists to come up with specific solutions that would work best in a particular region, most notably in areas where people rely on shark fishing to survive.
"They have no alternative... So we really need to figure out solutions that can work with those communities to still protect reef sharks effectively," says Chapman. “Robust shark populations can exist alongside people when those people have the will, the means and a plan to take conservation action.”
Zachary Huang-Ogata is a freelance writer specializing in science and the environment. His interests lie in sustainable resource management and corporate sustainability.