Of the 371 reefs surveyed in 58 countries, sharks were not observed on nearly 20 percent, indicating a widespread decline that has gone undocumented on this scale until now. The Global FinPrint team, led by researchers at Florida International University (FIU), also identified conservation measures that could lead to recovery of these iconic predators.

Essentially no sharks were detected on any of the reefs in 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 during more than 800 survey hours, according to the study published today in Nature.

"While Global FinPrint results exposed a tragic loss of sharks from many of the world's reefs, it also shows us signs of hope," said Jody Allen, co-founder and chair of the Paul G. Allen Family Foundation. "The data collected from the first-ever worldwide survey of sharks on coral reefs can guide meaningful, long-term conservation plans for protecting the reef sharks that remain."

This benchmark for the status of reef sharks around the world reveals an alarming global loss of these iconic species that are important food resources, tourism attractions, and top predators on coral reefs. Their loss is due in large part to overfishing of sharks, with the single largest contributor being destructive fishing practices, such as the use of longlines and gillnets.

"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," said Demian Chapman, Global FinPrint co-lead, associate professor in FIU's Department of Biological Sciences and researcher in the Institute of Environment. "We found that robust shark populations can exist alongside people when those people have the will, the means, and a plan to take conservation action."

The study revealed several countries where shark conservation is working and the specific actions that can work. The best performing nations compared 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 — being generally well-governed and either banning all shark fishing or having 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."

Launched in the summer of 2015, Global FinPrint's data were generated from baited remote underwater video stations (BRUVS) that consist of a video camera placed in front of a standard amount of bait – a "Chum Cam." Coral reef ecosystems were surveyed with BRUVS in four key geographic regions: The Indo-Pacific, Pacific, the Western Atlantic and the Western Indian Ocean.

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.

For more information and a new global interactive data-visualized map of the Global FinPrint survey results, visit https://globalfinprint.org.