A new study has found that some species of fish use sharks as scrub brushes to get rid of their parasites and other irritants, taking advantage of the sharks’ sandpaper-like skin.

The study was conducted by a collaborative research team led by the University of Miami’s Shark Research and Conservation Program at the Rosenstiel School of Marine and Atmospheric Science. They discovered different instances of fish rubbing up against a shark, a behavior that the team said is “frequent, widespread, and could play a previously unappreciated important ecological role for aquatic animals.”

The research team found 47 instances of fish chaffing themselves against a shark’s skin after examining underwater photos, video, drone footage, and witness reports.

“Although instances of fish chaffing against sharks have previously been observed, this study finds this cross-species behavior to be more pervasive than previously understood,” they said.

The research team said the chafing events were documented in 13 locations around the world. They recorded 12 fish chafing against eight different species of shark, including great whites. The number of fish exhibiting risky behavior varied from 1 to about 100.

“While chafing has been well documented between fish and inanimate objects, such as sand or rocky substrate, this [shark-chafing] phenomenon appears to be the only scenario in nature where prey actively seek out and rub up against a predator,” said Lacey Williams, a graduate student at the University of Miami, who co-led the study with fellow graduate student Alexandra Anstett.

Williams and Anstett used aerial drone surveys in Plettenberg Bay, South Africa, and documented 25 occurrences of fish turning to chafe against a passing great white shark.

The research team shared a video about their findings, which features the chafing behavior between different fish species and shark species.

It remains unclear why fish use sharks as exfoliators, but the researchers ventured a guess.

“While we don’t exactly know why it’s happening, we have a few theories. Shark skin is covered in small tooth-like scales called dermal denticles, which provide a rough sandpaper surface for the chafing fish,” said the university’s research associate professor Neil Hammerschlag.

“We suspect that chafing against shark skin might play a vital role in the removal of parasites or other skin irritants, thus improving fish health and fitness,” said Hammerschlag, a study co-author.

The study, titled “Sharks as exfoliators: widespread chafing between marine organisms suggests an unexplored ecological role,” was published in pre-print online on Oct. 28, in the journal Ecology, The Scientific Naturalist. 

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