Sharks use fish to stay clean, says Bangor research
Sharks make a big effort to be hygienic and swim to shallower waters to attract small fish which will remove parasites and tissue, research has found.
But this is viewed as risky because it leaves them vulnerable to people.
Bangor University scientists carried out work in the Philippines, concentrating on the endangered thresher shark.
It would come inshore to underwater mountains which are home to shallow water reefs.
This is where they interact with a type of small fish that grooms other fish species.
Bangor PhD student Simon Oliver, of the School of Ocean Sciences, said: "I equate it to having surgery if you had a head full of lice, and no way of removing them.
"Parasites are extraordinarily successful organisms and would propagate if the sharks had no way of getting rid of them.
"So these cleaning services are essential to the life history of these animals."
Mr Oliver thinks it is reasonable to infer that many species of sharks do this, both in tropical waters and possibly off the British coast.
In his work off the Philippines, he observed different species of shark visiting the same underwater mountains to be cleaned - an example of co-operative behaviour between animals.
"But what's unique about our [research] is that the clients we're looking at are large predatory animals," he said.
"It's like a lion at a waterhole with an antelope. Its thirst takes precedence over the natural order of things.
"The grey reef shark could easily take a bite out of a thresher, or a ray, but doesn't, which shows the necessity for these cleaners."
But this is not their only way of keeping clean.
"Another behaviour is breeching, where they launch themselves out of the water and slap back down," said Mr Oliver.
"I interpret that they are most likely again trying to dislodge parasites, especially those locked into their gills which aren't easily reached by the cleaners."
Dr John Turner, senior lecturer in marine biology and Mr Oliver's supervisor at Bangor, said: "The work uniquely describes why some oceanic sharks come into coastal waters to perform an important life function which is easily disturbed by man.
"Such knowledge will inform offshore industry, science, and conservation policy."
Mr Oliver has set up a shark research and conservation project to promote shark research.