1. Seal counts
The Farnes has the longest history of counting the seals of any colony. The work was started by the Natural History Society of Northumbria in 1952 (counts had been undertaken long before this but were only on certain islands). The Trust took over counting in 1970 and continues to this day. 2,737 pups were born in 2018 – this equates to a colony size of 9,580 based on multiplying the number of pups born by 3.5.
2. Seals in numbers
Male seals have a lifespan of 20-25 years and female seals have a lifespan of 30-35 years. Grey seals feed on wide variety of fish, squid, and octopus. They spend 80% of time below water, 20% on the surface breathing. Seal usually stay underwater for between 4 and 8 minutes at a time, although the maximum time recorded was 30 minutes. Seals can reach depths of 30 metres.
3. Counting the pups
Given the right weather conditions, the seals are visited every four days and new pups marked on the rump with a harmless vegetable dye. Using a rotation of three or four colours we can work out how many pups are born, how many die, and how many ‘disappear’ before they would be able to survive. This gives us the number born annually and allows us to calculate the mortality rate.