Seals heat up during moult
9 September 2009, by Tom Marshall
Harbour seals lose more heat to the atmosphere while shedding their fur coats, according to new research.
Each year, female seals move onto dry land to bear and suckle pups. A few weeks later, they start their annual moult. This helps keep their coats in good condition to protect them from harsh conditions at sea, but in the short term moulting costs them a lot of energy - for some kinds of seal, up to half as much as is needed to rear a pup.
During the moult, the seals' bodies become much warmer than usual. Infra-red cameras show hot spots appearing all over the seals' bodies during this period, with their average body temperature climbing more quickly and to a higher peak after they emerge from the water.
This means animals spend more time than usual out of the water as they moult. 'Our thermal images show that when moulting, their skin surface gets very hot,' explains William Paterson of the Sea Mammal Research Unit at the University of St Andrews (SMRU), lead author on the research.
'This is because they must circulate blood close to the skin surface to allow hair to grow quickly,' he adds. 'As a result, they expend a lot of energy during the moult and need to remain ashore for long periods. This is in order to maintain a high skin surface temperature that would not be possible without massive heat loss while in the water.' Paterson presented the findings at the British Ecological Society's Annual Meeting in Hatfield earlier this week.
Heat Seals
A team of scientists from SMRU, the University of Glasgow and Edinburgh Napier University used thermal cameras and CCTV to study two adult female harbour seals in captivity throughout the breeding season. They took thermal pictures every five minutes, while using CCTV to monitor how much time they spent out of the water.
'Unsurprisingly we found there was a peak in hauling-out during lactation, when the females needed to spend more time on land suckling their pups,' says Paterson. 'But we also saw a second peak when the animals were trying to maintain the optimum temperature for moulting.'
Temperature image of an adult female seal.
Paterson says that more effort should be made to reduce disturbance to seals during this period. Already, many haulout sites receive special conservation attention while seals are suckling young, and it could be beneficial to extend this treatment to the moulting period.
Seals disturbed during the moult will enter the water and shut down blood supply to the skin surface so as to minimise heat loss. This may prolong the duration of the moulting period and cause animals to expend more energy overall. This could mean they start the winter with inadequate fat reserves or coats that don't provide enough insulation.
Some UK seal populations have fallen by as much as 50% since 2000, so any measures that can improve their chances of surviving the winter are welcome.
The research also has implications for how seal numbers are monitored. Scientists at SMRU use aerial infra-red surveys to count seals, since the animals' natural camouflage makes them hard to spot with the naked eye as they lie on the shore.
At present, these seal censuses tend to take place in August and September, as animals haul out more to moult. Paterson's research confirms that this is probably the best time of year, as hot moulting seals show up better to airborne infrared sensors.
Paterson says the picture is likely to be similar for male harbour seals, although they often moult a little later than females. He also believes that similar conclusions will hold for other species such as grey seals, although these breed and moult at different times of year.
He hopes to follow this research up with a more complex study to quantify estimates of seals' metabolic heat loss more accurately.
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