New study builds on previous evidence that several reef shark populations have suffered deep decline, and their loss can have dire consequences on reefs and marine ecosystems.
A comprehensive study in the journal Science published June 15 2023, concluded that five key shark species are in serious decline and at higher risk of extinction. A team of 150 researchers surveyed almost 400 reefs around the world, and discovered that populations of these sharks suffered staggering declines of between 60 percent to 73 percent over the past half-century.
The team focused on five key species: the Caribbean reef shark, nurse shark, grey reef shark, blacktip reef shark and whitetip reef shark. Once the most abundant sharks on coral reef systems, these sharks are now entirely absent on a large percentage of reef systems globally.
The declines were calculated using models of what healthy reefs should look like, and measured those with varying shark abundance. The results were far worse in less wealthy nations with weak of lacking fishing regulations, or an absence of marine protection. The study found that sharks benefited in waters of wealthier countries and in areas with designated and enforced marine protected areas.
The 2023 study builds on a previous study of sharks on coral reef ecosystems published in the journal Nature in 2020, that discovered a complete absence of sharks on almost 20% of reefs evaluated worldwide.
Sharks Functionally Extinct From Reef Ecosystems
To better understand the level of shark disappearance across tropical and coastal reefs, an international team of scientists under the Global FinPrint organization revealed that sharks were virtually absent from almost one fifth of the world’s coral reefs.
The results indicate that sharks are too rare to fulfill their normal role in these ecosystems, also known 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 that time.
In that study, research biologists from the University of California, Santa Barbara conducted surveys at Palmyra Atoll, a Marine National Monument and American territory one thousand miles south of Hawaii. The UCSB team reported that sharks were far more abundant and the reefs were healthier in the marine protected area than in other areas surveyed. Healthy reefs like Palmyra provide baselines of health and relative abundance, giving context to the data collected from other reef systems. The data from a marine protected area helped establish what a healthy shark population and ecosystem without fishing looks like.
Support New Pacific Marine Sanctuaries to Save Sharks and Marine Ecosystems
Palmyra is part of an area, currently considered by NOAA under the Biden Administration, to expand the marine national monument around the Pacific Remote Islands by initiating National Marine Sanctuary designation. Like the proposed Papahānaumokuākea National Marine Sanctuary, Marine Sanctuary status will increase funding and protection for endangered species and some of the healthiest reefs in the Pacific Ocean.
Saving Sharks Will Protect Marine Diversity and Prevent Extinction of Other Species
Another 2020 study forecast dire consequences for marine ecosystems at current trends of extinction, and the loss of sharks will have the greatest consequence.
An international team of researchers examined the roles of marine megafauna species to better understand the potential ecological consequences of their extinction under different future scenarios. Extinction of threatened marine megafauna will lead to a huge loss in functional diversity in marine ecosystems, the researchers concluded. Sharks are predicted to be the most affected group, with losses of functional richness far beyond those expected under random extinctions.
The authors predicted that if current trajectories of extinction are maintained, we could lose, on average, 18% of marine megafauna species, which will translate in the loss of 11% of the extent of ecological functions in the next 100 years. However, if all currently threatened species were to go extinct, we could lose 40% of species and 48% of the extent of ecological functions.
According to the IUCN Red List, one third of all sharks, rays and related species are at risk of going extinct. The loss of apex predators also has impacts on fish down the food chain and the coastal communities that depend on healthy marine ecosystems for their livelihoods.
Coral reefs are struggling to survive from overfishing, habitat loss and a changing climate. Losing reef sharks can have dire long-term consequences for entire reef systems. These studies suggest we have hope for sharks and coral reef ecosystems if we can provide habitat protection and protection from fishing, but we must act now.
Widespread diversity deficits of coral reef sharks and rays. Colin A. Simpfendorfer et al Science 380,1155-1160(2023).DOI:10.1126/science.ade4884
MacNeil, M.A., Chapman, D.D., Heupel, M. et al. Global status and conservation potential of reef sharks. Nature 583, 801–806 (2020). https://doi.org/10.1038/s41586-020-2519-y
Overfishing drives over one-third of all sharks and rays toward a global extinction crisis Nicholas K. Dulvy, Nathan Pacoureau, Cassandra L. Rigby, Riley A. Pollom, Rima W. Jabado, David A. Ebert, Brittany Finucci, Caroline M. Pollock, Jessica Cheok, Danielle H. Derrick, Katelyn B. Herman, C.
C. Pimiento, F. Leprieur, D. Silvestro, J. S. Lefcheck, C. Albouy, D. B. Rasher, M. Davis, J.-C. Svenning, J. N. Griffin. Functional diversity of marine megafauna in the Anthropocene. Science Advances, 2020; 6 (16): eaay7650 DOI: 10.1126/sciadv.aay7650