Finding out about why not all young seals survive.

Johanna is a vet and pathologist carrying out a PhD on disease in grey seals between the Sea Mammal Research Unit in St Andrews and the Moredun Research Institute in Edinburgh. She is looking at causes of death among just born pups and, in particular, which bacteria, parasites and viruses they are carrying that may be shared with other species such as terrestrial mammals and birds. Grey seals are at the top of the food chain, live where the marine and terrestrial environments meet and as such may hold valuable information about the health of our marine coastal waters.
Although grey seals populations are relatively healthy, neonatal mortality is surprisingly high over the Isle of May colony, with 10-20% of pups succumbing in this period depending on the year. This year, she carried out post mortem examinations on seal pups that she found dead on the colony, looking to see if differences in causes of mortality depend on the type of ground the seals choose to pup on. Pupping areas stretch over the majority of the island and include the bouldery tidal beaches of Pilgrim’s haven, the grassy slopes of Tarbert and the rocky, muddy pools of Rona Rocks; so lots of different conditions to give each seal pup a very different start in life.
Infections of the umbilical cord were quite a common finding in seal pups in all areas of the colony – not a surprise though when you see how much time they spend in muddy pools! Here’s a picture of a rarer finding: enlarged thyroid glands (congenital goiter) in this newborn seal pup, the exact cause of which we have yet to look into. The thyroid gland (arrow) is almost 4cm long in this picture whereas it should be about 1.5 to 2cm long in a normal seal pup. In terrestrial mammals such as cattle, this can be caused by excessively high or low maternal iodine levels so that is something that remains to be investigated in grey seals.

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