Sharks are commonly heralded as an important species in oceanic and reef ecosystems, serving as an indicator of reef health, fish populations, and even seagrass growth. However, few people outside of the marine research community have noticed the alarming decline in shark populations, especially on reefs, until now, when it may be too late.
A July 2020 report published in Nature shocked many coastal communities across the globe when it announced that 20% of the reefs observed had no sharks over multiple months of observation. Although evidence of shark population decline had been previously recorded, the complete absence of sharks from multiple reefs across numerous countries and oceans confirmed what environmental researchers had been fearing: many species of sharks are becoming functionally extinct in the wild.
While functionally extinct does not mean fully extinct, a population that is functionally extinct is either no longer viable or unable to perform its specific role in the ecosystem it lives in, effectively ruining the natural order of the food chain, decomposition, and other regulatory processes.
Reef sharks play a vital role in their ecosystems, so what happens now that they are functionally extinct? Since sharks are generally considered the apex predator of their worlds, their removal triggers a “mesopredator release,” or increase in the populations of sharks’ prey. For reefs, this means an increase in middle-sized, predatory fish populations and a subsequent decrease in the number of their prey, smaller marine herbivores.
Many fishermen may like the sound of a larger-fish-rich environment — a place perfect for commercial fishing efforts — but the herbivores that these mesopredators feed on are equally as important in the ecosystem of a reef, as they regulate seagrass and algae levels. Without herbivores’ help to keep algae levels in check, the algae may grow out of control and suffocate young coral populations.
Since reef sharks are interconnected with the survival of young coral, protecting reef sharks is a crucial part of protecting our already-endangered coral reefs. In addition to the impact of coral reefs on marine environments, such as providing shelter and food for a plethora of species, over half a billion people rely on coral reefs for food, income, and shelter.
The functional extinction of reef sharks affects more than just reef environments. According to the 2020 report, there was a clear correlation between the size of nearby markets — places dependent on fishing and other marine trades — and smaller reef shark populations. This correlation is attributed to the alarmingly high rate of “by-catch,” which occurs when a shark or other species is unintentionally caught and killed by commercial fishing crews, and also to the growing demand for shark fin, considered a delicacy in many Asian countries.
Without these species of reef shark, both the fishing and tourism industries would suffer great losses. According to Oceana, a conservation effort based in Europe, one live reef shark can be worth over $250,000 over the course of its life as a result of diving tours, as compared to a one-time sale value of $50 when caught and killed. In addition, the negative effects of losing sharks in reef environments would decrease the value and attractiveness of those locations as tourist destinations, exacerbating the economic consequences on coastal markets.
Despite all these scary outlooks, the 2020 report was not all bad news. The report conveyed hopeful results about the effectiveness of “shark sanctuaries,” no-dive zones, and other conservation efforts. Areas with these conservation measures ranked highest in reef shark populations. The report specifically suggests that socio-economic policies aimed at decreasing by-catch and limiting the amount of shark products that can be caught and sold would be especially effective at expanding and ensuring that reef shark populations are protected.
If implemented now, these measures could “begin to restore the populations of reef sharks around the world,” the authors note, signaling that this report doesn’t have to spell the end of reef sharks. With help from economic sanctions on the sale of endangered sharks and the establishment of ecological sanctuary spaces, reef sharks still have a long future ahead of them.
This article was edited by Cat Kim and Emi Krishnamurthy.