Fausto De Nevi Herrera
The dire straits facing sharks around the world is a major theme in many gloom and doom predictions about the fate of the oceans. And there is plenty of reason for worry. Many shark populations are estimated to be at less than 10% of original levels, with some species possibly in danger of extinction. This is bad news not only for sharks, but for the many cultures that rely on them for protein in their diets.
Ecologists, too, warn of the effects of the decline in shark species and other top predators on ocean ecosystems. Eliminating sharks may induce what scientists call “ecological cascades,” where one effect induces another, and so on through the living world.
One example of that process is the rise in populations of certain rays – key shark prey – in regions where shark populations have declined. If there are too many bottom feeding rays, that may threaten seagrass beds and the shellfish that inhabit them. Those seagrass beds also serve as nurseries for many other species. So losing sharks may seriously degrade marine ecosystems, which could threaten the human fisheries tied to them. In addition, sharks can help control populations of invasive and exotic species – a growing problem as ocean ecosystems change.
And Now the Good News
Fortunately there is some good news amid all the bad. Careful fisheries management can help sustain shark populations. For example, spiny dogfish sharks, once seriously depleted in northeast United States waters, have come back much faster than expected and now support a greatly expanded fishery. Blacktip sharks in the Gulf of Mexico were just determined to be in healthy condition as a species, capable of supporting carefully managed fishing, including possible high-performance “catch shares” fisheries. There is even some evidence that great white shark populations along the California coast may be increasing in response to careful management and improving prey populations.
Individual nations are making important down-payments to help rebuild shark populations. Well-designed marine conservation areas and other types of shark sanctuaries can provide real benefits, if linked to sustainable fishing in waters through which sharks migrate. I have seen the potential first-hand, diving with abundant large sharks in Cuba’s Gardens of the Queen (Jardines de la Reina) National Park. But even there – more than fifty miles of the south coast of Cuba – sharks are taken when they wander outside the park, clear evidence that sustainable fishing must be tied to area-based management.
In addition, nations are beginning to work together to create joint solutions to the problem of preserving migratory fishes like sharks. The United States, Mexico and Cuba are sharing shark population information as a first step towards working together on a shared approach to managing sharks that migrate back and forth through the waters of the Gulf of Mexico. This tri-national program is in its early stages, but its potential is exciting.
So, if the news on sharks today is often bad, it isn’t always so. And the good news gives one a peek at a possible future in which populations of shark and other top predators are rebuilt, with the result that whole marine ecosystems will become more stable and resilient. There is much work to do, but a great vision is here today to power it.