Editor’s note: It’s Shark Week, which means we’re sharing some of our favorite stories about how the lives of sharks and other species — including humans — intersect. Today’s story underscores the many mysteries still hidden in the deep sea. Check out more Shark Week stories here.
A sei whale in search of its next meal sees the glowing outline of a fish. It swims toward the luminescent shape with its jaw open, ready to chomp, when the fish does something surprising: It suctions itself onto the whale with its lips and spins its body around, using its serrated teeth to remove a chunk of the whale’s flesh.
The perpetrator — called the “cookie-cutter shark” for the neat, circular wound it leaves — will bite whales, sharks, tuna — even humans — in its quest for food.
Researchers in South Africa are turning to the distinctive wounds inflicted by the cookie-cutter — also known as a “demon whale-biter” — as a new tool to understand the habits of the shark as well as its prey. They published their findings in April of this year in the open access journal PLOS ONE.
The researchers, Peter Best and Theon Photopoulou, analyzed wound data from more than 1,700 whale carcasses collected by Best at South Africa’s Donkergat whaling station in 1963. Despite the time lapse of more than 50 years since the data was collected, it still proved useful to the researchers: Because the whales were collected when commercial whaling was still legal, they provided a larger sample size than would normally be accessible to scientists today. Photopoulou explained: “The fact that the animals were dead allowed us to inspect the whole body of the whale, not just the sections that are visible when the animal surfaces to breathe.” This meant the researchers could review where on a whale the bites occur and determine when the attacks happened based on the stages of the wounds’ healing.
The “crater-like wounds” found on the four species of whale — sei, fin, Bryde’s and sperm — had confounded researchers for decades and been falsely attributed to other species. One sei whale alone had 183 unhealed bite marks. The researchers determined the culprit of the mystery bites was the cookie-cutter shark, a relatively elusive species given its small size (about half a meter long) and propensity for deeper depths (1,000-4,000 meters, or 3,300-13,100 feet).
Ultimately, the bite marks have provided the biggest revelations about whales: The paper states that the research showed the “whales are bitten regularly during the [Southern Hemisphere] autumn, winter and early spring,” indicating the whales had migrated away from the shark habitat by mid-spring. “The lower numbers of unhealed bites on medium-sized sperm whales suggests that this group spends more time outside the area in which bites are incurred, providing a clue to one of the biggest gaps in our understanding of the movements of mature and maturing sperm males.”
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The findings are only the latest evidence of how little we still know about the ocean and the life it contains.
“The ocean is like an antique pocket watch — you don’t see the intricate complexities that make it tick on the surface,” said Greg Stone, a marine biologist and executive vice president at Conservation International. “After thousands of dives over the past three decades, I am still surprised by the uniquely adapted creatures we encounter exploring the deep, like the cookie-cutter shark.”
Sophie Bertazzo is a staff writer for Conservation International.
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