Since the dinosaurs have roamed our planet, there have been sharks. These predators, swimming beneath our ocean’s waves, have survived numerous mass extinctions over the course of our planet’s history, and seem to have evolved to survive anything… except their most formidable opponent yet: us. For most people, an ocean full of sharks is their worst nightmare. But for those who study these animals, the reality of dwindling shark numbers is theirs.

Since the dinosaurs have roamed our planet, there have been sharks. These predators, swimming beneath our ocean’s waves, have survived numerous mass extinctions over the course of our planet’s history, and seem to have evolved to survive anything… except their most formidable opponent yet: us. Permission granted by Global FinPrint

Sharks face a staggering number of threats such as overfishing and bycatch, habitat destruction and degradation, climate change, plastic pollution, and illegal shark finning. In one of the largest collaborative projects yet, the impact these threats have had on our global shark populations has been made glaringly obvious: nearly 20% of the world’s sharks have vanished from reefs thought to be teaming with life.

Coral reefs were once renowned for being abundant with sharks, but these animals have been targeted by both legal and illegal fishers so that today many reefs see few, if any, individuals. By taking sharks out of these highly complex ecosystems, it has triggered a phenomenon called “mesopredator release,” where other large predatory fish will increase in abundance and feed on herbivores. If you’re a fisher, having more of these large fish (that you generally fish for) sounds like an awesome trade! But herbivorous fish are a vital component of this habitat, eating algae that would otherwise overwhelm and potentially kill young corals.

The study, published in the journal Nature, includes over 100 scientists working together to go through 15,000 hours of underwater video from 371 reefs in 58 countries, states and territories to show that sharks are absent on many of our coral reefs. In fact, this new research from Global FinPrint shows they are functionally extinct — which means they are so rare in certain areas they can no longer fulfill their role in the ecosystem. Since 2015, the Global FinPrint team — which is led by researchers at Florida International University (FIU) — has used underwater cameras to pinpoint specific strongholds for sharks and rays. 

In one of the largest collaborative projects yet, the impact these threats have had on our global shark populations has been made glaringly obvious: nearly 20% of the world’s shark have vanished from reefs thought to be teaming with life. Permission granted by Global FinPrint, Andy Mann

Guam, a USA territory, was among the worst-ranked locations identified in the survey. But how did the researchers rank each nation? With an Abundance Status Score, which ranks how viable a nation is for supporting the reef shark population against the size and proximity of the nearest market, poor governance, commercial fishing regulations, and other variables. “For most of our work, we looked at the maximum number of sharks that were in view of the camera at any time during a deployment. This makes sure that we don't count the same shark more than once,” explains Dr. Mike Heithaus, dean of the College of Arts, Sciences & Education (CASE) and Professor in the Department of Biological Sciences at Florida International University (FIU). “But, to get a sense of how well a nation is doing in terms of shark conservation, we needed to compare what we saw in the videos to what we would have expected without human impacts. The problem is that we don't have good baselines for what reef shark populations should look like in the absence of humans. It is possible that different regions (e.g the Caribbean, the Pacific, Indian Ocean) might have different baselines naturally. So, we created an ‘abundance score’ that compared the number of sharks we saw in a nation to the scores of all of the nations in the region. This score basically gives an indication of how the country does to the average in the region. Higher scores mean that a nation is among the best in the region, lower scores mean that sharks are much less common than the average.”

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. Only a combined total of three sharks were observed during more than 800 survey hours in these locations. But why so little sharks in these areas? “The specific reason for a lack of shark detections at each of these locations probably varies from place to place,” said Michael Berumen, Professor of Marine Science at the King Abdullah University of Science and Technology (KAUST). “Every country and every region faces its own set of challenges. As a broad generality, such a loss of sharks likely arises from overfishing or a lack of enforced regulations. [...] Another possible cause is a poor or degraded state of a location's reef; if the reef does not have a healthy community, shark populations may decline (for example, if there is not enough prey for them). These possibilities are not mutually exclusive - some places suffer from all of these problems at the same time.”

By taking sharks out of highly complex ecosystems like coral reefs, it has triggered a phenomenon called “mesopredator release,” where other large predatory fish will increase in abundance and feed on herbivores. This GlobalPrint footage is from the Bahamas in 2015. Permission granted by Global FinPrint

Thankfully, the study doesn’t only showcase bad news. For example, it also revealed countries where sharks are most abundant and where conservation measures are working — these locations include the Bahamas, U.S.A., Australia, the Federated States of Micronesia, French Polynesia, and the Maldives. Here, there are science-based management practices in place, like limiting how many sharks can be caught or banning shark fishing completely.

While this research identifies the primary culprits of reef shark population declines, it also outlines possible solutions for protecting and rebuilding reef shark populations worldwide. The researchers have numerous calls to action, like a call to action for more regulated commercial fishing on a global scale. “Reducing fishing mortality is key to protecting existing shark populations and rebuilding populations where they have declined. We found that there are several management options for effectively rebuilding shark populations including banning gillnets and longlegs, setting catch limits, and creating large protected areas or shark sanctuaries. Different options, or combinations of options, will work best depending on the particular context and nation,” said Heithaus.

Footage from the Global FinPrint project from 2017 in French Polynesia. In the Pacific Islands, sharks have long-held ecological, economic, and cultural significance, often representing an important god or deified ancestor. Global FinPrint

The scientists also want to draw attention to shark sanctuaries, as the presence of one in a given environment supported a 50% higher relative abundance of the species than nations without sanctuary status. “Shark sanctuaries have an advantage over the usual marine protected area (MPA) or marine reserve because of the limited size of most MPAs. Sharks may be too mobile for most small and medium sized MPAs to be effective. MPAs are boundaries drawn onto maps, and sharks have no way of knowing where these boundaries are,” said Berumen. “A national-scale sanctuary provides a greater level of spatial protection. [But] it is also important to note that, in cases where reef shark populations are indirectly depleted (for example, if the core problem is unhealthy reefs), even a national sanctuary alone may not be sufficient if the overall health of the nation's coral reefs is not also addressed.”

So what now? What can shark scientists do with the results of this collaborative work? “This study really opens up some intriguing and important areas for future work. On the scientific side, we are now working to use the data we have collected to understand how specific species have responded to human impacts and variation in reef environments,” commented Heithaus. “We are also working to better understand the ecological importance of sharks - and specific species of sharks - for reef ecosystems. Also, we now have a baseline of shark relative abundance globally using a standardized method. This will help us understand how fishing, climate change, and other impacts are influencing shark populations. We also can track how management might help rebuild populations. We also are planning to work with partners locally to ensure that the results of our study can be used to help improve shark population numbers, reef health, and the well-being of the communities that rely of reef ecosystems.”

Here’s hoping we can turn things around... others we might see these special sharks vanish completely.