Monday 14th November comments: As part of ‘Seal Season’ we bring you the story from the researchers who have been working with the Grey Seals on the island since late October. Scientist Kimberley Bennett takes up the story;
Every year the Isle of May not only hosts a large grey seal colony, but it is also temporary home to researchers interested in the seals. This year there are 12 of us, from Abertay University in Dundee, Durham University, the Sea Mammal Research Unit (SMRU) at St Andrews University and Université de Liège in Belgium. We’re here to find out more about the ecology, behaviour and physiology of grey seals. Physiology is the science of how animals work and how their bodies’ systems deal with challenges, from cells right the way up to the whole animal. Seals are amazing animals from this point of view. They can hold their breath for 30 minutes while diving, gain fat very rapidly and go for extended periods of time without food or water while they are on land during the breeding season.
A female feeds her single pup on milk that can be as much as 60% fat, and she does that without eating at all for the whole 18 days on the colony! No wonder the pup can triple its body mass in that time, going from around 15 kg at birth to around 45 kg at weaning. Late in the suckling period, the pup begins to moult into its ‘adult’ pelage, which is much more sleek and waterproof and a lot less fluffy than the beautiful white ‘lanugo’.
Feeding the pup takes its toll on Mum, who loses 40% of her body mass, and once she’s mated she leaves the island to feed up again out at sea. In the meantime, the pup stays on the colony with no food for about 9 days, up to as long as 40 days in some cases! This period of fasting on land is important for pups to develop their ability to dive: red blood cell number, muscle oxygen storage capacity and breath holding duration all increase. The pups have to use up fat from their blubber to fuel their metabolism during fasting and until they learn how to feed for themselves once they go out to sea.
You can see that fat really important for seals. Blubber keeps them warm, provides fuel for metabolism and helps with streamlining and buoyancy. Pups that are fatter are more likely to survive their first year and fatter females are more likely to raise a fat pup. Fatter adult males are bigger, which makes them better able to win a fight and able to stay on the colony longer, which increases their chances of mating. The problem of being so fat and so reliant on it to be healthy is that some chemical pollutants found in fish accumulate in the seals’ blubber.
We already know that very high levels of these pollutants cause problems for immunity, development and may even cause cancer in seals. At lower levels, the pollutants may affect hormone signals and alter how fat tissue works. Our NERC funded project aims to understand how these pollutants affect the rate that pups build their blubber layer, the rate fat is used when they are fasting, and the way blubber responds to hormonal signals.
This will help us better understand how marine pollutants affect survival in grey seal pups. It will also help us predict the effects the same pollutants will have on body fat in people. If you’re interested in what we do and would like to know more, check out team member Kelly’s blog, PHATS and SMRU websites and the Durham team blog.