When the fearsome megalodon became extinct, it may have been because it didn’t have enough food.
Unlike most sharks, the star of the 2018 film, “The Meg”, had a large appetite due to its warm-blooded nature - like its descendant, the great white shark.
Most other shark species are cold-blooded fish, or so it has been thought until now.
However, newly published research led by Trinity College Dublin (TCD) scientists has discovered that the basking shark found in Irish waters and another “Meg” descendant, the smalltooth sand tiger, may also have warm-blooded traits.
The scientists have described it as both “surprising” and concerning, as this may reduce the ability of these species to cope with warming seas.
Their findings follow the results of tests conducted on live basking sharks off the west Cork coast, along with autopsies of the bodies of three small tooth sand tiger sharks washed up on Irish and British coasts earlier this year.
Dr Nicholas Payne of TCD’s School of Natural Sciences is senior author of the study, published this week in the journal, Biology Letters.
Trinity College Dublin marine biologist Dr Haley Dolton tagging a basking shark off the west Cork coast. Results from temperature measurements of the basking shark show it also has warm-blooded traits. Photo: Dr Haley Dolton
As he explains, the three small tooth sand tiger sharks are a deep water species and a rare occurrence in these waters as they are not normally found north of the Bay of Biscay.
“We don’t know why they stranded, but the team in Britain did a lot of autopsy work,” he said.
During this research, it was found that the smalltooth sand tiger sharks had red muscles close to the vertebrae and a high percentage of compact myocardium in the ventricle heart – both being key signs of warm-blooded physiology.
Payne’s TCD colleague and lead author of the study, Dr Haley Dolton, found the same traits in basking sharks while conducting tagging on the large plankton-eating fish off the west Cork coast.
Known in Irish as “ainmhí sheoil” or “the beast with the sail” due to its dark fin, the basking shark is a protected species under the Wildlife Act.
She explains that body temperatures of basking sharks were measured in the tagging project, which took place with the West Cork Charters skipper David Edwards off Courtmacsherry, Co Cork.
Dr Payne describes the findings as very important, as it may mean that several other shark species also have “regional endothermy” or warm-bloodedness.
“This raises plenty of new questions as to why regional endothermy evolved, but it might also have important conservation implications,” he says.
“We know the seas are warming at alarming rates again now and the smalltooth tiger that washed up in Ireland was the first one seen in these waters. That implies its range has shifted, potentially due to warming waters, so a few alarm bells are ringing,”Dr Dolton adds.
The research team also included scientists from University of Pretoria, Zoological Society of London, University of Zurich, Swansea University, Smithsonian Tropical Research Institute and University College Dublin.
Dr Dolton’s work was funded by the Irish Research Council and Dr Payne was funded by Science Foundation Ireland.
