Reef sharks were always thought to be in perpetual motion, but a new study suggests sharks can nap or sleep.
The study is based on grey reef sharks in the Seychelles, and has been published in the Journal of Fish Biology.
As it explains, sharks use gills to breathe, applying two methods. Some sharks, called obligate ram ventilators, ‘ram’ oxygen-rich sea water over their gills and need to keep moving to do so, the paper says.
Other species, called buccal pumpers, actively pump sea water over their gills while stationary, it says.
The study entitled ‘Just keep swimming? Observations of resting behaviour in grey reef sharks Carcharhinus amblyrhynchos’ overturns existing knowledge, the authors state.
“The grey reef shark is an endangered reef dweller in the family Carcharhinidae and was the quintessential representative of a shark that moves to breathe,” according to the Save Our Seas D’Arros Research Centre (SOSF-DRC) in Seychelles.
“On routine survey dives around D’Arros we found grey reef sharks resting under coral reef ledges,’ the centre’s director of research, Dr Robert Bullock, says.
‘This is not something we believed they could do. The grey reef shark has been considered a ram-ventilating species, unable to rest, so to find these ones resting, turns our fundamental understanding of them on its head,” he said.
The researchers say they encountered grey reef sharks resting alone and in groups at different sites around Seychelles.
“And through it all, the sharks seemed blissfully unaware of their observers,”they say, remaining still, except for lower jaw movements that suggest the ram-ventilating sharks can switch to buccal pumping behaviour.
Craig Foster, founder of the SeaChange Project, was one of the divers and authors of the paper.
“There is something very special about “tiptoeing” around underwater at a depth of 25 metres and looking into the open eyes of sleeping sharks, moving carefully so as not to wake the peaceful beauties,”Foster says.
Save Our Seas Foundation chief executive Dr James Lea said that the findings were “key to understanding how they use their environment and also how this may change in response to shifts in environmental conditions”
Founded in Geneva, Switzerland, in 2003, the Save Our Seas Foundation (SOSF) is a philanthropic organisation which states that its ultimate goal is “to create a legacy of securing the health and sustainability of our oceans, and the communities that depend on them, for generations to come”.
Its support for research, conservation and education projects worldwide focuses on endangered sharks, rays and skates. Three permanent SOSF research and education centres are based in Seychelles, South Africa and the USA.
