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Sharks and their relatives are some of the most threatened vertebrates on Earth, with approximately one-third estimated or assessed as threatened with extinction. This is a major problem because as predators that help keep the food web in balance, these animals play a variety of vitally important ecological roles and in doing so help to keep healthy many ecosystems that humans depend on. Coral reefs provide homes for countless fish species that are vital for fisheries and are therefore an especially important ecosystem for humans—and one where the decline of shark populations seems to be especially acute. On page 1155 of this issue, Simpfendorfer et al. report the results of a species-level and reef-level analysis of common resident reef sharks across the world. They show startling declines of once-common reef shark species but also signs of hope that these populations can recover with the right protection.
The study by Simpfendorfer et al. is the result of a worldwide collaboration called the Global FinPrint project. The data analyzed include more than 20,000 hours of standardized underwater video taken at nearly 400 reefs in 67 countries and territories around the world—that is nearly 3 years of raw video. The baited remote underwater video stations (BRUVSs) used by FinPrint are a simple but powerful tool. They are essentially underwater camera traps that consist of a small quantity of bait suspended in front of a camera. In addition to being good at documenting the presence and absence and the behavior of different marine organisms, they also generate high-definition images and video of marine life that are tailor-made for public education about what lives in the threatened habitats off our coastlines.
The results of Simpfendorfer et al. reveal declines of 60 to 73% of once-abundant coral reef shark species at reefs around the world. This adds to a large and growing volume of similarly alarming conclusions about the global conservation status of sharks and their relatives. The global conservation status of sharks and rays is worse than a decade ago and is even more concerning for some groups of sharks. Sharks caught as bycatch in global tuna fisheries are declining in population even as those same tuna are rebounding.
However, the findings of Simpfendorfer et al. include signs of hope and a clear path forward. Their results show that although shark populations in many reefs had declined, some healthy reef shark populations remained. The reefs with healthier shark populations had some important similarities: They tended to be in the waters of high-income countries with stronger natural resource management regulations, participatory natural resource management (where citizens have the right to petition the government about changes in natural resource management policy), and resources for enforcing the rules. Unfortunately, such countries are relatively rare, and lower-income countries tend to have fewer resources for sustainable management and enforcement. These observations show that conservation problems involve solving human problems as well as those associated with ecology; a country that lacks the resources to feed its people is less able to sustainably manage and protect its biodiversity.
Science-based, well-enforced marine protected areas—in which harmful fishing practices are restricted or banned—also tended to have healthier reefs. However, Simpfendorfer et al. suggest that some highly touted shark conservation solutions were enacted in places where there were not many threats to the shark population to begin with and advise caution in interpreting the success of those solutions. For example, the British Virgin Islands shark sanctuary bans all commercial shark fishing in its territorial waters, but between 1950 and the 2014 establishment of the sanctuary, only 3 tons of shark were fished from those waters, suggesting that there was not much of a shark fishery to ban. Another sanctuary was established in the Bahamas in 2011 but decades after the most common shark fishing gear was already banned, suggesting that the country’s relatively high shark population is most likely due to the older, less-hyped regulation.
The most unexpected result of the study by Simpfendorfer et al. is that a decline or complete loss of shark species in one reef was not always associated with similar changes in nearby reefs. They found that one reef can be overfished so badly that a once-common reef shark species is totally gone, but another reef a short distance away can have healthy populations of that same species. Strong, effective management (including but not limited to no-fishing-allowed marine protected areas) on one reef protected local species, even while their populations on neighboring reefs faced collapse. The presence of these possible future “source” populations—that is, healthy populations that can eventually help repopulate nearby areas—gives hope that if the threats that led to population decline are resolved, then these important and threatened animals may recover.
The study by Simpfendorfer et al. also demonstrates the growing importance of global collaboration. Global problems require huge multidisciplinary teams because scientists or laboratories working by themselves simply cannot generate or analyze data on this scale. In many ways, FinPrint has been a model for international collaboration. Such studies have documented how the decline of sharks leads to increasing abundance of mesopredatory fishes such as moray eels, what aspects of marine protected area design are most effective for sharks, and much more—and there is more to learn.
The problem is clear—animals that provide ecosystem services that are vital for human food security and livelihoods are disappearing at an alarming rate, overwhelmingly owing to bad management practices that allow unsustainable overfishing of these ecologically important and biologically vulnerable creatures. The loss of sharks and the ecosystem services they provide represents an ecological disaster that can cause substantial harm to humans. Action must be taken to prevent further population declines and allow rebuilding of depleted populations before it is too late.
Associated study
- Colin A. Simpfendorfer et al. Widespread diversity deficits of coral reef sharks and rays. Science380, 1155-1160 (2023). DOI:10.1126/science.ade4884
TL;DR
Simpfendorfer et al. 2023 studied coral reef shark population. Shark population down 60-73%, bad. High-income countries with good natural resource management are good for sharks. Global collaboration needed.