At the end of last term we had a university trip to Donna Nook, located in Lincolnshire. Every year between October and December thousands of grey seals migrate to the salt marshes of the reserve to mate and breed.
Salt marshes are a valuable ecosystem which maintain a vast number of rare species populations, and perform several important ecosystem services and functions. However, threats to these landscapes including pollution, coastal development and invasive spices endanger their conservation. Despite this, during our latest university trip to Donna Nook, conservation was not our main focus. Instead, we were interested in the seals social behaviour, and the differences between the three groups of individuals; males, females and pups.
The grey seal, Halichoerus grypus can be found in several large colonies across Britain and Ireland, with colourations varying from dark with lighter patches, to very light with darker markings. In order to breed, large but varied landscapes with minimal disturbance are required. They rely on cold waters to feed, living off a diet mainly consisting of fish, squid and crustaceans. They themselves however, sit fairly high at the top of the food chain. They were the first mammals to be protected by modern legislation, as British colonies are of global importance; their only natural predator in British seas is the killer whale.
Each year females produce one pup at around 15kg in size, and covered in a white coat for warmth. Parental care for seal pups only lasts for around three weeks before the pup is left to fend for itself. During this time they are fed by their mother, lose their fluffy white coat and triple in size. Once the pups coat has been shed it is able to swim in the sea, where eventually pups are forced by hunger to migrate. According to research carried out by the University of Plymouth, 2017, pups have a critical period of around 40 days in which to find food, and learn perfected hunting skills. A split in approaches as to how this is achieved is seen between males and females. Within the welsh populations studied, females were shown to dive in shallower water where attempts are generally more successful. With no size difference at this age to the females, it is thought that the cause of this separation is caused by the physiological processes males undertake in the progression to adult life.
Soon after leaving her pup, due to a long gestation period of eleven and a half months, and delayed implantation of up to three months, females must quickly mate once again. In order for a grey seal female to mate she must be at least four years old. With each male mating with several females constant fight break out between bulls, for both dominance and territory. Female grey seals are also often seen to be aggressive, something we observed several times on our trip. Previous studies in to this behaviour have shown this aggression may be resultant of two different female goals. With aggression greatest in the first lactation period, protection of the pup is a likely explanation. Secondly, a hypothesis that being aggressive increases the chance of mating with a dominant male, displays a kind of female choice.
The conservation of seals act currently protects grey seals, however individuals seen to be damaging fishing equipment can legally be killed. The conservation of sites like Donna Nook helps ensure the species survival, and with over 2,000 pups born at the site each year (2,066 this season so far!) it is hoped this will continue for years to come.
For more cute seal pup photos and videos you can look at my gallery on the home page or my video page!
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