Researchers working off of the Revillagigedo Archipelago south of the Baja Peninsula in the Pacific Ocean have documented Galapagos sharks (Carcharhinus galapagensis) rubbing their bodies against oceanic manta rays (Mobula birostris) in order to remove external parasites.
Sharks have been known to use surfaces to scrape off parasites and often make use of the 'cleaning services' of smaller fish that pick them off. They also perform manoeuvres such as breaching that may serve to dislodge external parasites. And other species of fish such as tuna are known to rub against sharks to remove unwelcome hitchhikers.
However, the new research, published on the preprint server BioRxiv in April 2025, records the first observations of sharks using rays to get rid of pesky hangers-on.
Between December 2024 and February 2025, two juvenile sharks and one adult shark were seen scraping their bodies on the undersides of passing manta rays for the first time. While a few of these parasites may be an annoyance to the shark, they can eventually become a serious problem.
“One of the most common ectoparasites found on sharks are copepods. Copepods are small crustaceans that attach to the skin, fins, or gills and feed on mucus and tissue,” explains lead author Jane Vinesky. “These organisms are small but mighty. Carrying them in excess can severely impact the health and fitness of the host over time.
"In our observations, sharks primarily scraped their heads, faces and lateral sides against mantas,” she adds. These areas are prime targets for parasites, according to previous research.
The efforts of the juvenile sharks did not appear to bother the rays (see footage below), but the ray approached by the adult shark attempted to flee (see footage above).
These observations occurred near known 'cleaning stations', where sharks and other fish are serviced by species such as the Clarion angelfish (Holacanthus clarionensis). These smaller fish scan the bodies of their larger relatives for parasites and pick them off. The 'client' fish wait calmly, displaying no aggression or feeding behaviour while they are cleansed of their unwelcome guests.
However, populations of Clarion angelfish have declined and dive tourism may inadvertently disrupt the dynamics of cleaning stations. The authors speculate that sharks may turn to more proactive measures when cleaner fish are in short supply.
"More sharks may be competing for space at cleaning stations, leading some individuals to seek out less competitive alternatives like mantas,” adds co-author Mauricio Hoyos.
Image and video credit: Credit: Vinesky et al.
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