It’s now a very busy time in the breeding season and the island is coverd in grey seals of all ages, from newborns to females over 30 years old. The first weaners (pups who’s mothers have weaned them by going back to sea to eat fish, typically at about 18 days after birth) are starting to appear at the edges of the colony, without their mothers to protect them from aggressive adult seals the weaners quickly retreat to the peripheries of the colony. Even with so many seal pups of different ages around, it is still possible to tell approximately how old a seal pup is just by looking at it. It’s not always easy, but knowing the ages of the seal pups on the island is really important information for the various scientific projects studying the seals. For behaviour and physiology projects, it is crucial to know the developmental stage of a pup you are studying. For population dynamics research (which keeps track of the abundance of speices and detects changes in the numbers of individuals around our coast) knowing how long seal pups are present on a colony helps scientists accurately run models estimating pup production, an important variable in the model representing seal population changes around Scotland.
So how do you tell how old a pup is just by looking at it? Here is a crash course! Pups are divided into stages based on their appearence and the stages correspond to approximate ages (described here and drawn here). There are five stages in all, covering newborns to pups that have weaned and are independant from their mothers.
These pups are the youngest on the colony, and this stage covers pups that are newborn up until about day 5 of life. Things to look out for include a pink, squishy umbilical cord from the pup’s stomach and pronounced shoulders protruding from the pup’s back as they are quite skinny when they are born. The back slopes distinctly away from the shoulders down towards the tail, and sometimes they have dried blood from birth in their fur.
These pups are between 6 and 9 days old. Their umbilical chord has dried up and if it is still present, it looks withered and black. The pup will have increased it’s blubber layer just under the skin from drinking fat rich milk from it’s mother, so you won’t be able to see the shoulder blades easily any more. The back of the pup will still have a slight slope from the shoulders towards the tail, and there will still be a dip at the neck of the pup.
Pups within this stage are between 10 and 16 days old and are substantially fatter than the previous two stages. The back of these pups is almost flat because of how much blubber is covering the lower abdomen, and these pups start to look a little like barrels. The dip at the neck will have gone, but the pup will still be entirely covered in white pup fur called lanugo.
These pups can be very distinctive because it is defined by the pup losing (moulting) it’s white fur. As soon as a pup starts to moult the white lanugo, it becomes as stage 4 pup. The pups usually start to moult around their faces and flippers first, then the rest of their body follows over a few days. If the pup rubs against rocks or other seals then the white fur can come out in large patches at one time, revealing the adult fur underneath which is often patterned with spots. These pups are between 17 to 24 days old. At day 18, mothers typically wean their pups so you can see ‘weaners’ with half moulted white coats around the edges of the colony.
This is the last stage, and includes any pup that is more than 25 days old. These ‘weaners’ have no lanugo left on their body and can vary in colour from very pale, to spotty, to pure black. Weaners often stay on the breeding colony for several weeks after their mothers leave, which is called the post-weaning fast because they don’t have anything to eat while they remain on the colony without their mothers. To get food, they have to go to sea for the first time and learn to catch fish. This means that the amount of fat a pup puts on while it’s with its mother is very important for it’s survival; the fatter a pup is, the more blubber it has to burn for energy and the more time it has at sea to learn to catch fish before it starves. We still don’t really know why pups stay on the colony after weaning for so long as they often lose several kg of blubber during the post-weaning fast.
Being able to tell the age of pups is very important for the PHATS team as we are only interested in pups that are very close to weaning or have weaned from their mothers already (read our blog here for more details about why we sample the seals at these particular times). We have just identified our first study weaner, who is a stage 4 pup that has been dubbed ‘Charlie’ from the phonetic alphabet as her study code is ‘C’. We will be keeping an eye on her for the next two weeks during her post-weaning fast, so stay tuned for updates about her in the coming weeks!
In the tissue culture lab on the Isle of May we have received several samples from pups that are about to wean from their mothers and have been successful in keeping the cells alive for the PCB and hormone exposure experiments we are carrying out. To make sure that the cells are alive during the experiments, we sent some of our tissue back to the PHATS laboratory at Abertay University back on mainland Scotland. To do this, Dr James Turton extracted RNA (ribonucleic acid) from the fat tissue in our experiments and determined it’s integrity by putting it on a gel and applying an electrical current to separate out the different sized molecules in the RNA (know as gel electrophoresis). RNA is a vital component of all living cells, it is how DNA (Deoxyribonucleic acid) in the nucleus of cells transfers information to other parts of the cell so it can function normally. If the fat cells died during the experiment, the RNA would degrade and would not show up on the gel. Thankfully our cells were all alive and showed clear white bands of intact RNA on the gel after the test, confirming the RNA has good integrity and the cell in our experiment were alive. Hooray!
The other research on the island is also progressing well, Dr Sean Twiss from Durham University has been working in collaboration with Dr Patrick Pomeroy from the Sea Mammal Reseach Unit at the University of St Andrews to trial UAVs (unmanned aerial vehicles) for use in seal research. As they fly high over the colony they have the potential to be able to see areas of the island that we otherwise could not study, however the high winds that often blow over the Isle of May can make flying the UAVs difficult! Read more about Dr Twiss’ research on his blog about seal behaviour here.
MEANWHILE away from the seals, the epic cooking and baking continues! I baked batches of fresh bread rolls for a monster hand-made burger night when it was my turn to cook for the masses. Dr Twiss engineered an incredible sushi evening for dinner over the weekend, almost too pretty to eat! Last night we had a stunning roast leg of lamb, which PHATS team member Holly was in charge of, so good.
Ouside of the kitchen I’ve been amusing myself by working on my sketching skills, doodling various birds that I’ve seen on the island in my sketchpad between all the lab work. Hopefully by next weekend I’ll have a whole menagerie in my book!