Ten facts about the Farne Islands' seals
The Farne Islands are home to thousands of grey seals (also known as Atlantic seals), and each autumn hundreds of pups are born here. Here are ten facts about seals on the Farnes from one of the head rangers.
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.
Storms can be devastating for seals, particularly those from the north which can strip pups from some of the low-lying islands causing mass deaths. However, seals on some of the higher islands such as Staple and Brownsman are less prone to wave-wash.
5. Hungry mums
Grey seals are ‘capital breeders’, which means that during their stay at the colony in the autumn both females and males fast, obtaining all their energetic requirements from their blubber. Female fasts can be over 20 days, while male fasts can be over 50 days. The longer a male can stay in the colony and defend his territory, the more successful they will be.
6. The first few weeks
It's tough being a seal pup. 30% of pups die within a month and 50% within their first year. Pups are weaned in 18 days, in which time they will have quadrupled in weight. Abandoned by their mother, they spend another 20 days or so on the colony before heading out to sea for an independent life.
7. Tracking and technology
The first experiment in tracking seals was on 16 December 1951 when ten pups were fitted with metal cattle tags. One was found alive at Jaeren, 20 miles away from Stavanger, Norway on 30 December. The pup travelled 400 miles in a maximum of 14 days. This was the first clue that seals moved across the North Sea and such large distances.
In 2017 Farne Islands rangers experimented with drones to capture seal pup numbers from the air. As part of this work we carefully monitored the response of the seals to the drones. This year we are repeating this experiment as it's much less intrusive for the seals and much less dangerous for the rangers.
8. Monks and seals
From the 12th century onwards, the seals were harvested by the Islands' monks. They were valued because of the oil that could be extracted from their carcasses and also as a luxury food. As creatures of the sea, seals counted as ‘fish’ and so could be eaten on a Friday. In 1378-79 a seal calf could fetch about 22p which works out at about £140 in today’s money. From documents through to the 1500s there was quite a trade in seals and seal products.
9. The Farnes and other colonies
The Farnes is one of the third largest colonies on the east coast of England. 2.5% of the annual British pup production is from the Farnes, compared to 20% from the Monach Islands in the Outer Hebrides – the largest British colony.
10. Other seal species
Very small numbers of common seals (also known as harbour seals) can be found on Holy Island, with small numbers around Teesside, then larger colonies around the Wash. They are very rare on the Farnes with an average of 1 recorded per year.