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Altered habitats

At the beach this summer, celebrate shark sightings

Winter has finally waned, store mannequins sport bathing suits, New Englanders are pondering their travel brochures for a beach vacation, and thoughts are now turning to ... sharks.

Pity the poor shark.

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Every swim season we can expect a flurry of dramas over the sighting of a few sharks off the coastline. Beaches are closed, spotters are launched in small planes and helicopters, land-stranded swimmers are asked by reporters to exclaim their fears, and the headlines blare the threat.

But the biggest threat is to the sharks. We’ve all seen the statistical proof of our silliness: we have less chance of being killed by a shark than by a toppled vending machine; twice as many Americans die of alligator attacks, and you are 11 times more likely to be killed by fireworks than a shark, and about eight times more likely to be bitten by a squirrel.

But what is less well known is how ruthlessly we are killing off sharks. We are engaged in the rapid extermination of many shark species, and largely for indefensible reasons: to flavor shark-fin soup, or as discarded accidental “by catch” of industrial fishing, or shot as a sport encouraged by the sharks’ menacing reputation.

A recent study by 23 scientists led by the Shark Specialist Group, a scientific arm of the International Union for the Conservation of Nature, concluded that “overfishing and habitat degradation have profoundly altered populations of marine animals, especially sharks and rays.”

The group noted, in a paper published in the online journal ELife, that only one-third of the many shark species are considered numerically safe. At least one-quarter of the species are threatened or endangered, and so little is known about shark numbers that the estimate may be way off. The actual fishing mortality of sharks, for example, is estimated by the scientists at three-to-four times the numbers officially reported. Several shark species “have not been seen for many decades,” the report noted.

Sharks, like many top predators, grow slowly, mature late, and produce few offspring, which they protect for long periods. They are among the oldest vertebrates on earth; their lineage goes back 420 million years. But the geologically sudden appearance of an even greater predator -- man -- makes their slow reproduction a fatal vulnerability.

Overfishing and accidental by-catch are the chief threat to sharks, followed by habitat loss, persecution, and climate change, the group said. Of the intentional catch, “a main driver ... is the globalized trade to meet Asian demand for shark fin soup, a traditional and usually expensive Chinese dish.” Sharks in shallow coastal areas, such as those along the Atlantic, are most vulnerable.

“Many governments still lack the resources, expertise, and political will necessary to effectively conserve the vast majority of shark and rays,” the authors noted.

We should bemoan the loss. Moral philosophizing aside, top predators, including sharks, serve a crucial role in ecosystems. Take away the sharks, and you have what scientists call a “trophic cascade.” The fish on which sharks dine, suddenly free of their nemeses, explode in population. The smaller fish that those species eat suddenly find they are lunch for the multitudes, and their populations plummet. And so on. The result is ecosystem chaos and more loss of biodiversity.

So when you are at the beach this summer and the alarm is raised over a shark sighting: rejoice. There are fewer and fewer of them left.

Doug Struck has been a journalist for 35 years and reports on environmental matters from Boston. He can be reached at doug@dougstruck.com.
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