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A Caribbean reef shark passes a BRUVS in the Bahamas. (Photo courtesy Andy Mann)

  • The world’s largest reef shark survey allowed researchers to get a snapshot on how reef shark populations are doing around the world
  • Researchers behind Global FinPrint were surprised by the number of places with relatively healthy shark populations 
  • The scientists say the study will provide a road map to help restore reef shark populations
  • Their results are having impact; based on the data they were able to collect, countries have already changed their management plans to protect these animals

Decades of overexploitation have put our ocean’s sharks at the precipice of extinction. 

Thanks to the efforts of over 120 researchers and at least 730 volunteers, the world’s first-ever benchmark status on reef sharks has been published by scientists behind Global FinPrint. What they uncovered, after more than 15,000 hours of footage in 58 territories and countries, revealed the profound impact that fishing has had on reef sharks. Sharks were absent on nearly 20% of the reefs they surveyed, including entire nations altogether. 

We spoke to the lead investigators of the Global FinPrint project, Florida International University’s Drs. Mike Heithaus and Demian Chapman, and Dalhousie University’s Dr. Aaron MacNeil, about the study, the surprises they encountered, and the hope they see in protecting reef sharks for the future. 

Why count reef sharks? What threats do they currently face?

Dr. Mike Heithaus: We know that sharks are being removed from oceans at an unsustainable rate overall to satisfy the demand for fin and meat. But to know where sharks are in trouble, where they are doing well, and where we can have the most impact if we intervene, we had to get out there and count. 

It’s actually pretty surprising how little data there were on reef sharks when we started. Global FinPrint allowed us to get a snapshot of how sharks are doing on reefs worldwide using the same methods.

After nearly five years surveying almost 400 reefs in 58 countries around the world, what were your biggest takeaways and surprises from the survey?

Dr. Demian Chapman: In the years immediately before Global FinPrint, my primary research focus had been on the shark fin trade in Hong Kong. My first walk in the dried seafood district there was overwhelming. I saw the remains of more sharks in one afternoon walking a few city blocks than I had underwater in the previous 15 years in the field. I couldn’t fathom how we could possibly have any sharks left with this level of ongoing trade. 

When I started setting BRUVS (Baited Remote Underwater Video Stations) for Global FinPrint and seeing what the other field teams were bringing in, I was extremely anxious that we would see nothing but water, small fish, and plastic bags in all but a handful of places. Instead, we found that there were more refuges for sharks than we had thought, even if many other places did live up to my worst fears. Overall, it became clear that the impact of people in communities nearest the reefs we surveyed was the primary factor influencing local shark populations. This is good news in a sense because it means that the battle to keep sharks for future generations really is in our hands.

How was Global FinPrint able to cover as much territory as it did? 

Chapman: The beauty of Global FinPrint is that our core team of scientists sat down very early on and came up with a simple survey process: drop BRUVS in random spots for 60 minutes each and do everything in the same way, everywhere. Our team of 121 scientists then went to hundreds of reef locations and dropped BRUVS around 40 times at each. Environmental variables such as depth, temperature, and seafloor structure were measured. 

The data collection didn’t end on the water though. We also went into the community and asked questions about how people interacted with sharks on each reef: for example, did they fish sharks? If so, what kind of gear did they use and what sort of management measures were in place? Our team studied the national laws that were in place related to sharks and collected national human population and economic data.

What were some of the biggest obstacles you faced? 

Chapman: The sheer scale of Global FinPrint was the biggest obstacle. At the heart of it, we had to organize teams in 58 nations and territories all to conduct a shark survey in exactly the same way. Once we got that going we had to find a way to detect and count all of the sharks that occurred on more than 15,000 hours of video that were captured. To put that in perspective: if you watched all of the video data that we collected back-to-back it would take you two years to see all of it! At the end of that process, Dr. Aaron MacNeil and his team had to organize and model a very large and complicated dataset. Although I spent many sleepless nights worried about how we could get all of this done, at the end of the day the vast team of people we assembled made this happen through force of will and a love for sharks and our oceans. 

Dr. MacNeil, tell us more about your team’s analysis? It seems complicated so give us the cereal box version of how you did it?

MacNeil: Statistical models always seem complicated but this is really just about counting sharks and calculating the average number seen on each reef. To do that well you have to account for things like sampling conditions, which can skew our estimates, and for fishing conditions, which affect the number of sharks in the water. 

We developed what’s called a Bayesian hierarchical model to do this, which allowed us to account for these things at various scales, from reefs within nations and nations within regions, and make our best guess as to the maximum number of sharks we would expect to see on a reef anywhere in the world.

Since this is the first-ever survey of its kind, how do we know if reef shark populations are increasing or decreasing as you say in the study? 

MacNeil: In the majority of places we don’t know for sure, because regular surveys aren’t typically done. However, my experience studying reef fisheries suggests that there will be a mix of both increases and decreases, with ongoing declines in the majority of places. You have to keep in mind most reef fisheries are in developing nations where coastal people are highly dependent on reef fish for food and income, yet governance and management may be lacking. These conditions tend to generate overexploitation that extends to sharks as well. 

What’s important about this study is that it gives us a place to start. The next survey will reveal a trend and a third survey will tell if the trend is real and so on. Having a baseline to start with is the only way to know for sure and that baseline is what Global FinPrint has achieved. 


What impact do healthy shark populations have on our lives and livelihoods? 

Heithaus: You can’t have a healthy planet if you don’t have healthy oceans. And, we are learning that sharks can play a role in having healthy ocean ecosystems. In other studies, we have found that losing sharks could lead to collapses of ecosystems so they support less fish and shellfish that people harvest and could even change the amount of carbon dioxide that is removed from the atmosphere, because sharks effectively keep seagrass from being overgrazed by the species that sharks eat and scare. We still don’t know enough about how sharks affect coral reefs, but sharks may help keep the reefs themselves intact and help promote healthy populations of fish. And beautiful reefs and healthy fish populations provide food and fuel ecotourism industries.

This isn’t just a science project. It is an example of how we can work together — science, NGOs, government, and local communities — to make science-based decisions that will support the natural world and people. 

Dr. Mike Heithaus

How do you see Global FinPrint’s results being used in the future?

Chapman: In the immediate future Global FinPrint’s results are going to provide a road map on where we should focus reef shark conservation efforts and which measures we should put in place in these nations. We are already seeing scientists, NGOs, and governments all over the world using our results for a variety of conservation-related activities. 

One of our primary questions when we first started was what happens when sharks are removed from coral reefs? We know that the removal of large predators on land has triggered major and often unexpected changes in the ecosystem, so we are interested in learning what happens when large predators are lost in the ocean. 

This knowledge will help governments justify shark conservation investments and allow us to predict the broader consequences of overfishing or restoring sharks. We trained and equipped teams in over 30 nations on how to do these surveys, which will allow local people to see how their conservation actions translate into more animals on their reefs.

What are you most proud of when sharing with others about this study?

Heithaus: There is no question I am most proud of the incredible level of collaboration that occurred to make this happen. We built a network of scientists that will continue to work together to answer important questions and provide the science to ensure that shark populations remain healthy where they are doing well and are rebuilt where they are in trouble. The project has also supported a lot of young scientists around the world and built our global capacity to work on sharks, rays, and reefs. I am also incredibly proud of the impact we are already having. To see countries like the Dominican Republic and Belize change their management plans to protect these animals based on the data is really encouraging. This isn’t just a science project. It is an example of how we can work together — science, NGOs, government, and local communities — to make science-based decisions that will support the natural world and people. 


What gives you hope that we can reverse the decline facing sharks? 

MacNeil: What gives me hope is our human capacity to solve seemingly intractable problems. From climate change to the response to Covid-19, our ability to break problems down to the local scale and build-up solutions that work in varying contexts means that there is a similar way forward for reef shark conservation. The hard part is of course how to get it done - if people are unable or unwilling to change then it’s not going to happen - those things have to come first. But once people are on board, research from projects like Global FinPrint have identified a range of solutions that can be tested and tweaked to local conditions, ensuring shark populations persist for years to come.