When a sandy patch becomes a shark scratching post

Learning about chafing behaviour

The world of sharks is full of unknowns. It invites people around the world to dive in and explore. For those of us who allow ourselves to be seduced by this world so unfamiliar yet so close to us, several questions can arise. How do sharks behave? What is their role in the oceans? What are their vulnerabilities? How do they interact with other species, especially with humans? There are many more questions, some of which have already been answered, and others are yet to be discovered. The current question on my mind is: how do sharks clean themselves? This is the subject of the research that I am presently carrying out within the Charles Darwin Foundation’s “Shark Ecology” research project.

Scalloped hammerhead shark being cleaned by juveniles of the Mexican hogfish. Photo © Ana Moya.

Early in 2022, we went on a field trip to the northern and eastern islands of the Galapagos Archipelago, where we deployed underwater video cameras at several reef fish cleaning stations. When analyzing the footage, we observed the interactions where one fish cleans another individual (client-cleaner relationship) and unusual behaviour, where individuals of different shark and fish species scratched various sections of their bodies against a rough surface, such as rocks or sand. To my surprise, this behaviour has been more common than it sounds and is known as chafing. This behaviour by elasmobranchs and other fishes has been previously reported as a cleaning strategy to remove parasites from different parts of their bodies, including the edge of the mouth, the tips of the pectoral fins, and the ventral area.

Galapagos shark chafing the edge of its mouth on a sandy patch at Wolf Island. Photo © Ana Moya.

One event, in particular, caught our attention when a group of scalloped hammerhead sharks (Sphyrna lewini) entered a sandy patch and swam very close to the bottom, suddenly a male shark chafed its claspers (male reproductive organs) against the sand as he continued swimming, demonstrating his agility to bend over, exposing his claspers, chafe them and continue within the group formation. This event is described in more detail in the manuscript “Chafing behaviour by scalloped hammerhead sharks (Sphyrna lewini), including an unusual scratching of claspers”, recently published in the journal Marine Biodiversity.

Unusual behavior of a Scalloped hammerhead shark chafing its claspers on a sandy patch at Wolf Island. Photo © Pelayo Salinas.

Although this event was unusual for us, the scratching behaviour of claspers is likely an important activity for maintaining these reproductive organs in a healthy condition for the mating events that have been confirmed to occur in the Tropical East Pacific (TEP).

It is clear that in the world of sharks, there are complex interactions, such as cleaning interactions, which play a key role in maintaining the health of marine organisms. They take many forms, such as client-cleaner interactions and the use of inanimate elements, such as stones or sandy patches, and certainly others that have not yet been observed. This is only the beginning of our exploration of shark cleaning behaviour at the Galapagos Islands. We will surely find more surprises to uncover as we continue fulfilling sharky dreams.