Study finds sharks are ‘functionally extinct’ in 20% of reefs observed

While most people would find a face-to-face encounter with a shark terrifying, humans are a greater threat to sharks than they are to us. And overfishing and exploitation have depleted species in many of the world’s ocean reefs, a new study shows.

Despite their image as feared marine predators, sharks are themselves hunted for their meat and fins, which are a sought-after delicacy in some countries. Many are simply in the wrong place at the wrong time, ending up as by-catch in fishing nets set for tuna and other fish species or caught up in drifting 'ghost nets' long abandoned by fishermen.

But in some parts of the world, conservation efforts are protecting shark populations, providing optimism for the future of a creature that has been around for hundreds of millions of years.

Human impact

Using video footage taken at more than 370 reef locations in 58 countries, researchers assessed the conservation status of sharks in different parts of the world. The study’s results, published in the scientific journal Nature, show an absence of sharks in 20% of the reefs surveyed. This is largely due to destructive and unsustainable fishing techniques – sharks have few offspring and mature slowly, leaving them vulnerable to overfishing.

The study found a strong relationship between reduced shark numbers and the proximity, density and poverty levels of the nearest human communities. Some poorer societies were found to be highly dependent on shark meat for food, for example, while ineffective governance failed to prevent overfishing, leaving sharks “functionally extinct” in eight of the countries surveyed.

Underwater videos recorded by the study team reveal a very different picture in countries such as the Bahamas and Australia, with strong management of fisheries and marine sanctuaries in place. In these places, the report describes “increased abundances of reef sharks”.

Occupying the top of the marine food chain, sharks help maintain balanced ocean ecosystems. Having few natural predators, sharks limit the populations of their prey, switching from one food source to another depending on what’s available. This ensures biological diversity by preventing one type of prey growing too dominant and disrupting things further down the food chain.

Almost a third of all species of sharks and rays face extinction, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, part of a mass extinction threat looming for many land and marine animals. So, what can be done to protect shark populations?

Effective action

Sharks were found to thrive in countries that enforce marine protection areas, which prevent commercial fishing in certain places or for particular marine species. Shark fishing has been banned in the Bahamas for more than three decades, for example, helping the country lead the world in shark abundance, according to the report.

Effective marine management can include regulating fishing activity so sharks are caught less frequently, either intentionally or as collateral catch. Alternatively, legislation could be enforced banning harmful fishing techniques: gill nets are almost invisible to the multitude of marine species they entrap; and long-line fishermen trail hundreds or sometimes thousands of hooks in the water for long periods to catch fish indiscriminately, a technique which could be replaced with a more targeted approach.

Similarly, the US and EU have enforced bans on the practice of removing shark fins at sea then discarding the carcass, reducing catch numbers by insisting the whole fish is brought to shore before removing the fins. Yet the illegal trade in shark fins persists.

Dr Andy Cornish of WWF points to the need to make the trade in shark products more transparent and more traceable, rejecting products from unsustainable or unknown origins in order to clamp down on illegal trade.

“Far too few people realize how bad the shark crisis is, and how much more costly and difficult solutions become the longer we delay. We must ask ourselves: Are we prepared to accept the consequences — moral, ecological, and economic — of letting dozens of species of sharks disappear forever on our watch?” he wrote on Medium Environment.