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Sevengill shark
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In Graphic Detail: Sharks in Parks

Some marine reserves are unintentionally helping coastal sharks thrive.

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by Brishti Basu

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New Zealand has 44 marine reserves in its territorial waters. All are no-take zones: no fishing of any kind and no resource extraction. Though intended to protect overfished species—snapper, blue cod, spiny lobster, for instance—the reserves likely provide cover for a range of other species, including sharks. For decades, coastal shark numbers have been declining and some species face extinction. The number of tope sharks around the world, for example, has dropped by 80 percent in the past three generations—due to commercial fishing.

For their study, the scientists visited five marine reserves in the Fiordland (Te Moana o Atawhenua) Marine Area, southwest of New Zealand’s South Island; the reserves are no bigger than 40 square kilometers, or about two-thirds the size of Manhattan, New York.

To spy on shark populations, scientists deployed 167 baited remote underwater video (BRUV) systems—waterproof cameras framed in stainless steel with pipes connecting them to bait-filled containers—inside and outside the boundaries of the marine reserves. They dropped half the cameras in the reserves and the other half into surrounding unregulated waters. The BRUVs regularly lured four shark species: one top predator (the sevengill) and three mesopredators, sharks in the middle of the food chain (spiny dogfish, tope shark, carpet shark).

Graph showing abundance of shark species inside and outside of marine reserves

This graph shows the number of sharks counted in five relatively small marine reserves (blue bars) compared with sharks counted outside the reserves (orange bars). The final bars are the sum of the three mesopredator sharks (spiny dogfish, tope shark, carpet shark). Graphic by Heldsinger et al.

The researchers found that mesopredator sharks are thriving in the reserves, likely because they, and the lobsters and fish they eat, are protected from fishing. These relatively small marine reserves, however, make no difference to the top predator that regularly grazes the BRUVs, the sevengill shark.

The researchers think the limited sizes of the marine reserves—which range from 4.3 to 36.7 square kilometers—offer no advantage to sevengill sharks, which have large hunting grounds and likely roam far outside the protected areas.

The findings suggest that to protect far-roaming species like sevengills, marine parks need to be at least the size of the sharks’ regular stomping grounds.

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Cite this Article:

Cite this Article: Brishti Basu “In Graphic Detail: Sharks in Parks,” Hakai Magazine, Mar 17, 2023, accessed June 24th, 2024, https://hakaimagazine.com/videos-visuals/in-graphic-detail-sharks-in-parks/.

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