The first two weeks of our field season on the Isle of May have been very busy ones, and we’re now well into the research that we need to get done on the island. In the last week the colony hit peak pupping time, which meant there was lots of amazing births to watch on the island. So, in honour of all the little lives I’ve witnessed come into this world over the last 2 weeks, this blog will be about the wonders of seal pregnancies and births. Births and young pups are fascinating to observe, but please keep in mind that all the observations and photographs we take are done under permit and from hides during research on the breeding colonies as part of scientific projects. Please do not approach or disturb seals during autumn, as they may be pregnant or with pups. Mothers may abandon pups if people come too close, and then the pups will starve to death.
Birth is usually a rapid process in the grey seals here on the Isle of May; we often observe females give birth within ten minutes of visibly starting to push! Many females come to the island prior to giving birth, and either hang around the rocky coast of the island or make forays into the colony in the days before pupping. Female grey seals also show site fidelity (i.e. they go back to the same spot) to the place where they give birth, so we can not only find the same females every year on the Isle of May, but they are found in almost exactly the same places year after year with their current pup. Once a female has given birth to her pup she will usually instantly turn around to begin nosing and sniffing the pup, beginning the bonding process that will keep her by its side for the next 18 days. Grey seal mothers only have 18 days to nurse their pups before they must return to sea. Females don’t eat while they are on the colony, so they loose lots of weight while they are producing fat rich milk for their pups, usually dropping about a third of their mass from when they arrived at the island.
Seal pregnancies are very different to human ones, as they can delay implantation of the growing embryo in the womb, so that it stops developing for a certain time period before it implants and the pregnancy continues normally. This enables grey seals to give birth at the same time every year, despite mating when they leave the colony on day 18 and having pregnancies than only last about 9 months. Many species of mammals, especially carnivores, show delayed implantation, or embryonic diapause, and it is widespread in the pinniped species (seals, sea lions and walrus). However, recent research has found some seal species, like the Weddell seal that lives in Antarctica, may not have delayed implantation. New studies to understand the environmental, nutritional and population pressures driving the evolution of delayed implantation in types of seal will hopefully help us figure out why some species have this physiological adaptation and others do not.
Birth and rearing a young infant is always a testing time for a mammalian mother, and in marine mammals, newborn infants face an additional challenge to their wellbeing. Marine mammals typically have high persistent organic pollutant (POP) burdens due to their top trophic positions in the food chain and the bioaccumulation of the POPs in predators. As these substances are lipophilic (they combine with fat tissues in the body, like blubber) this means that infant marine mammals are at risk from the pollutant burden of their mothers. Some transfer of POPs occurs during pregnancy across the placenta, but once the pup or calf is born, mothers have to produce fat rich milk to feed their offspring with. To do this, mothers typically mobilise the fat reserves in their blubber, and as this tissue has high POP concentrations, these go into the milk she’s producing. By having to drink milk with elevated POP concentrations, newborn marine mammals are continuously ingesting proportions of their mother’s pollutant burden up until they wean, which can have serious negative impacts on their immune system and chance at survival. The PHATS team I’m currently working with is trying to uncover more about the physiology underlying the impact POPs have on fat tissue function and an individual’s ability to generate and utilise blubber properly. By using novel tissue culture techniques in wild breeding colony locations (LINK), we’re hoping to provide new insights and develop new methods to investigate physiological problems caused by such man-made changed to the environments.
MEANWHILE I’d like to introduce you to some of our study seals! They are all named after the phonetic alphabet, and we watch them from birth, to weaning and beyond to gather data and samples from them. This means that at any one time, we have white coat pups that are still with their mothers, pups that have just weaned and are moulting their white baby fur (or lanugo) and pups that are well into their 1-4 week post-weaning fast, with their spotty adult fur. Below are a few of our study seals, and I’ll post updates about how they are all doing on the blog every week.