The ocean is full of interactions we never get to see. Not because they are necessarily rare, but because the open ocean beyond coastlines and reefs is enormous. Although it is all encompassed in our little blue marble of a planet, animals can still easily disappear into blue water within seconds. Trillions of encounters happen hundreds of miles from shore, and researchers may spend years at sea and witness only fragments of them and these marine animals’ lives. So when the same unusual behavior begins appearing again and again in different corners of the world, scientists start paying attention. And that is exactly what is happening with sharks rubbing themselves against other large marine animals.
A new study from Mexico’s Revillagigedo Archipelago led by Jane Alban Vinesk documents Galápagos sharks (Carcharhinus galapagensis) scraping against oceanic manta rays (Mobula birostris), adding another piece to a growing puzzle about how sharks maintain their skin health and how marine ecosystems may be changing around them. These interactions were recorded between December 2024 and February 2025 at two well-known dive sites within Revillagigedo National Park, a protected marine reserve in the eastern tropical Pacific. Divers captured video footage of Galápagos sharks approaching manta rays and deliberately rubbing parts of their bodies, especially their heads, gill regions and sides, against the mantas’ undersides. And this is not the first time scientists have noticed sharks doing something like this. In recent years, researchers have documented silky sharks, grey reef sharks and Galápagos sharks rubbing against whale sharks in places like the Maldives, the Galápagos Islands and Revillagigedo itself. Silky sharks have also been observed scraping against manta rays near Malpelo Island off Colombia. Taken together, these sightings suggest the behavior may be more widespread than scientists initially realized.
But as with many emerging behavioral records, there is an important scientific caution here: interpretation depends on perspective. “It’s important to distinguish between what is new to us and what is genuinely new in the system,” says Dr. Madalena Pereira Cabral of Cuidando los Mares de México A.C. “The fact that we are only now documenting this behavior does not necessarily mean it is a recent development — it may well have been part of the ecological dynamics of this system for a long time.” In other words, we may be witnessing discovery rather than emergence. And this matters because the ocean is becoming more observed than ever before: more divers, more cameras and more long-term ecological monitoring mean behaviors that once passed unnoticed are now being recorded. Vinesk rebuttled Cabral’s assessment, saying, “Revillagigedo has undergone decades of intensive diver observation, particularly of manta rays. My opinion is that if sharks had been routinely scraping against them for years, it is very likely someone would have filmed it before now. The fact that we are only documenting this now is itself meaningful data. Since publication, multiple researchers and divers have reached out to let me know they observed the same behavior recently, so it also appears more widespread than we originally thought.”
Regardless, the behavior itself raises interesting biological questions. Many large marine species already use multiple strategies for parasite removal, including cleaning stations and scraping against substrates or other animals. Sharks are known to rub against reefs, sand, rocks and even the seafloor to remove irritants. In open water, where hard surfaces are limited, other large animals may simply become convenient alternatives.
Cleaning stations like those in Revillagigedo are central to this system; manta rays regularly visit these sites to be cleaned by reef fish. Each cleaning requires stillness, trust and time as cleaner fish remove parasites and damaged tissue from across the body, making them sensitive to disturbance. But when people approach too closely, blocking movement paths or surrounding animals for photographs, it can interrupt this “spa day” process. Animals can shorten or abandon cleaning events altogether. This has led some researchers to consider whether human presence might be influencing these interactions; one possible factor contributing to the observation rather than the emergence of rare shark behaviors is the ecological context created within well-enforced marine protected areas. These sites often concentrate both wildlife and tourism, bringing together dense aggregations of animals and people in the same space. “In that context, interpreting these observations as evidence of disruption requires caution,” argues Cabral. At present, she says there is no direct evidence demonstrating that cleaning-station function has been reduced or altered in a way that would induce a change in shark behavior. Some of the sites where these interactions have been documented are also deeper cleaning stations that are rarely visited by divers, which further complicates assumptions about human influence.
Ecologically, the behavior seen here may simply reflect flexibility. These interactions are better understood as part of a wider suite of interspecies behaviours, reflecting behavioural flexibility and the use of alternative cleaning strategies. Truly, it’s a general principle in our natural systems: animals improvise. Sharks are not locked into a single strategy for parasite removal, likely shifting between methods depending on what is available in the moment. If cleaning stations are crowded? If cleaner fish are less accessible or if movement costs are high? Well, alternative strategies like scraping against other large animals may become more common. Behavioral flexibility is one of the most important traits animals can possess in rapidly changing environments! And it is very different from adaptation. While we tend to think of adaptation as something that happens over evolutionary timescales, behavior can shift much faster; for example, a shark does not need thousands of years to start using a new scraping surface if the opportunity presents itself. The larger question, though, is whether these improvised behaviors are sustainable or beneficial for everyone involved. Parasites go beyond being just a mere inconvenience; ectoparasites can irritate skin, damage tissue and potentially increase infection risk. They may also affect swimming efficiency or overall health, particularly in large migratory animals already expending enormous amounts of energy moving across vast distances. Finding ways to remove those parasites is of vital importance. But while the sharks may gain relief from parasites, yes, the costs to manta rays remain unclear. Repeated scraping could create stress, disrupt feeding or cleaning behavior or potentially transfer microorganisms and parasites between species. What begins as a possible response to ecological disruption could eventually reshape relationships between animals sharing these habitats.
“For me, the most exciting part of what we documented at Revillagigedo is a shark recognizing another animal as a potential tool and using it deliberately, targeting specific body regions where parasite loads are highest,” says Vinesk. “That requires the shark to assess its environment, identify an opportunity, and act on it. Elasmobranchs have repeatable personality traits like individual boldness and sociability, and our observations suggest that mantas are doing the same kind of individual-level assessment, deciding whether a particular shark poses a risk worth evading. These are not simple animals running on instinct, but making choices based on their experience.”
The question is not simply whether sharks are behaving differently, but why we are only now seeing this behavior so clearly. At the center of this debate is a familiar tension present in the natural sciences: are we witnessing a system under stress or simply seeing it more clearly for the first time after years of protection and closer observation? Are we witnessing ecological change, or are we only now beginning to understand how these species behave and interact in their natural environment?
The most honest answer, for now, sits somewhere in between. What is clear is that interpretation matters.
