But hope lies in key conservation measures.
Though many people find them intimidating, menacing or just plain scary, sharks are vital to the health of the world’s oceans.
These often misunderstood creatures are found in just about every ocean habitat around the globe, but their populations are plummeting. Indeed, the true extent of their decline is not fully known.
To better understand the level of shark disappearance across tropical, coastal reefs, an international team of scientists conducted a landmark study under the Global FinPrint organisation. Their findings, published in the journal Nature, reveal that sharks are virtually absent from many of the world’s coral reefs.
The results indicate that sharks are too rare to fulfill their normal role in these ecosystems — otherwise referred to as “functionally extinct.” Of the 371 reefs surveyed in 58 countries, sharks were not observed on nearly 20%, suggesting a widespread decline that has gone undocumented on this scale until now.
“Things aren’t good for sharks,” said coauthor Darcy Bradley, co-director of the Ocean and Fisheries Program at UC Santa Barbara’s Environmental Market Solutions Lab. Scientists have known this for a while, she added, but this study shows it in robust, empirical detail.
Where are sharks missing?
Essentially no sharks were detected on any of the reefs of six nations: The Dominican Republic, the French West Indies, Kenya, Vietnam, the Windward Dutch Antilles and Qatar. Among these, a total of only three sharks were observed on more than 800 survey hours.
And where is shark conservation working?
The study revealed several countries where shark conservation is working and the specific actions that seem promising. The best performing nations, in comparison to the average of their region, included Australia, the Bahamas, the Federated States of Micronesia, French Polynesia, the Maldives and the United States.
These nations reflect key attributes that were found to be associated with higher populations of sharks. They are generally well-governed, and either ban all shark fishing or have strong, science-based management limiting how many sharks can be caught.
“These nations are seeing more sharks in their waters because they have demonstrated good governance on this issue,” said Aaron MacNeil, lead author of the Global FinPrint study and associate professor at Dalhousie University. “From restricting certain gear types and setting catch limits, to national-scale bans on catches and trade, we now have a clear picture of what can be done to limit catches of reef sharks throughout the tropics.”
The FinPrint team is wrestling with the fact that conservation action on sharks alone can only go so far. Researchers are now looking at whether recovery of shark populations requires management of the wider ecosystem to ensure there are enough reef fish to feed these predators.
“Now that the survey is complete, we are also investigating how the loss of sharks can destabilize reef ecosystems,” said Mike Heithaus, Global FinPrint co-lead and dean of the College of Arts, Sciences & Education at Florida International University. “At a time when corals are struggling to survive in a changing climate, losing reef sharks could have dire long-term consequences for entire reef systems.”
Over the course of four years, the team captured and analyzed more than 15,000 hours of video from surveys of 371 reefs in 58 countries, states and territories around the world. The work was conducted by hundreds of scientists, researchers and conservationists organized by a network of collaborators from Florida International University, the Australian Institute of Marine Science, Curtin University, Dalhousie University, and James Cook University.
MacNeil, M.A., Chapman, D.D., Heupel, M. et al. Global status and conservation potential of reef sharks. Nature (2020). https://doi.org/10.1038/s41586-020-2519-y