The seals' skin surface gets very hot during moulting
Thermal imaging technology has been used to show how seals' skin heats up to help them shed and regrow hair during their moulting season.
William Paterson of St Andrews University followed two adult female seals from late pregnancy to the moult.
He said that harbour seals spent more time out of the water while moulting to avoid losing too much heat.
And he said growing new hair used up half as much energy as was required to rear a seal pup.
Mr Paterson said his study showed that people should try not to disturb seals when they were moulting.
"Emphasis is given to try and not disturb harbour seals during the pupping period as mothers suckle their young, and the same treatment should also be afforded to these animals during the moult period," he said.
"Disturbances would increase the seals' energy expenditure and prolong the duration of the moult.
"The implications would be that there would be less time available for foraging as the animals head into winter and they may have less fat reserves as a result."
Harbour seals, like most mammals, re-grow some or all of their hair each year.
Mr Paterson, of St Andrews University's sea mammal research unit, used thermal imaging techniques and CCTV during his study of the annual moult between August and September.
Thermal images show the hotspots where the seals are re-growing hair
The project, funded by the Leverhulme Trust, also involved Edinburgh Napier University and Glasgow University.
It measured the body surface temperature of two adult harbour seals as they hauled out of the water onto land.
He said the annual moult often went undetected for marine mammals such as seals, but it was important for maintaining their health and condition while at sea.
Mr Paterson said: "Our thermal images show that when moulting, their skin surface gets very hot as they must circulate blood close to the skin surface to allow hair to grow quickly.
"As a result, they expend a lot of energy during the moult and need to remain ashore for long periods to avoid becoming chilled in the cold water."