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October 2016    Download the Entire Issue (PDF) Available to the Public Vol. 31, No. 10   RSS Feed for Undercurrent Issues
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Reef Sharks – Are They Over-Valued?

from the October, 2016 issue of Undercurrent   Subscribe Now

An article by science writer Alex Riley in Hakai Magazine asks the question,"Are we over-valuing reef sharks?" He makes the point that the movie JAWS made everyone think that all sharks are apex predators with a degree of power over environment that, in the vast majority of cases, they've never really held.

He quotes the New Yorker: "We've been systematically killing off sharks, in spite of evidence that, as 'apex predators,' they're crucial to maintaining biodiversity," or Wired: "Drive keystone predators like sharks extinct and entire ecosystems collapse."

He says that this is patently not true and cites ecologists Peter Mumby and George Roff saying that the familiar tale of devastating losses of sharks through fishing and finning crippling the wider ecosystem is often just a story, not a conclusion backed by science.

In 2004, researchers from the University of California, San Diego, published a study that assessed the inter-relationships of 208 species of fish inhabiting a Caribbean coral reef. What ate what, and which species got the benefit? The research computer model suggested that by eating mesopredators (grouper and trevallies, for example), sharks that inhabited the reef increased the number of herbivores like parrotfish, thereby controlling the build-up of algae.

Mumby, Roff, and colleagues compiled 11 classic studies on coral reef ecosystems, looking for evidence of the reef shark's presumed influence, but what they found ignored this conventional wisdom. In areas where sharks were fished, herbivore numbers didn't fall. In Marine Protected Areas where large-scale fishing is banned, a bounty of sharks didn't lead to a plethora of herbivores.

Of the 26 key species of sharks on coral reefs, only a few infrequent visitors (namely tiger sharks, bull sharks, and hammerheads) can be placed in the top tier of the food chain. 'Shark' isn't a blanket term for a huge voracious hunter, but a family of cartilaginous fish that encompasses a diversity of diets and lifestyles. The vast majority of species, such as whitetip reef sharks and gray reef sharks, for example, are more akin to large-mouthed groupers and giant trevally in their eating habits. They are all merely mesopredators and less crucial to the ecology of the reef.

Many divers want to see sharks, and in some areas of the world, shark diving accounts for a significant proportion of a small nation's gross domestic product. For us, they are important indeed. For the reef, perhaps fishermen aren't such a bad thing.

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