Updated: Jul 17, 2021
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Anyone that knows me knows about my OBSESSION with seals– so much I spent time studying them, diving with them, rescuing them, and even running a half marathon to raise money for them!
After being a member of the British Divers Marine Life Rescue (BDMLR) marine mammal team, and my time at the Cornish Seal Sanctuary, I learnt that some injuries came from human disturbance – which upset me. This led me to study the impacts of disturbances on grey seals (Halichoerus grypus) living on the North-Coast of Cornwall.
In this article, I will not be naming any specific locations as I wish to protect the grey seal colonies in Cornwall from future disturbances!
Human disturbance on marine megafauna has impacted the functional diversity of marine ecosystems and has resulted in climatic variability and sea-level oscillations. Therefore, it is important to evaluate the effects of human activity which interferes with marine wildlife, by observing behavioural responses.
With increasing tourism demand, seal colonies are often exposed to intense visitation levels from humans. In 2002, the United Kingdom Tourist Survey found 16.4% of holiday trips in England involved wildlife watching.
Great Britain represents ~40% of the world’s seal population and 95% of the European seal population, however, despite being abundant in Britain, numbers elsewhere have decreased with some in Europe listed by IUCN as endangered-which is very heart-breaking news to me!
Seals are from the family Phocidae, known as pinnipeds, referring to sub-aquatic mammals with all four limbs adapted into flippers. Their body shape is round with lowered limbs, and a body covered in a large store of blubber to keep them warm. Grey seals have a flat nose profile compared to a common/harbour seal (Phoca vitulina), which has a more rounded face with a distinct forehead. Grey seals are more ‘dog-like’ and common/harbour seals more ‘cat-like’.
Grey seals can be seen in Cornwall all year round, however, harbour seals are seen less frequently and in smaller numbers. Grey Seals have a larger body size averaging at 1.8 to 2.1 m long, whereas harbour seals only grow up to 1.7 m.
The breeding season in Great Britain occurs between September to December, however, pups have been found all year round in South-West England. They must return to the land (haul-out sites) to give birth and provide for their young.
The moulting season in Great Britain starts in January and usually ends in May, followed by the hunting season (June-August) which focuses on fattening them up.
This means the seals spend more time at offshore haul-out sites, therefore disturbances must be reduced during this time. However, in Cornwall, this is the busiest time for tourism, so disturbances are unfortunately common and affect their natural behaviour.
The ability to haul-out is extremely important to restore the grey seal’s energy levels. When hauled-out grey seals tend to be seen in large groups and become vocal by making a ‘howling’ noise in response to disturbance. The ability to haul-out is also important for predator avoidance, skin growth, and maintaining a core temperature.
Bycatch is the accidental capture of animals in fishing gear, which can have detrimental effects on marine mammal populations, and other marine life!
In 2015 the total annual seal bycatch (from gillnet fisheries) was estimated at 580 seals, this is a 39% increase since 2014. During this year, 15 bycaught seals were reported, 13 of which, sadly were grey seals.
Entanglement causes injuries from debris such as plastic, which often results in death. Many seals during my disturbance study were sadly entangled in plastic, mostly from nets and frisbees.
Vessel propeller wounds are unfortunately also fairly common. They create corkscrew lacerations and in the year 2000, 8 out of 100 seals were reported dead with this type of wound.
Photo by Zoe Lucas
Globally, Atlantic grey seals are a rare species, and so have become a major tourist attraction in the South-West of England representing 22.8% of all domestic trips in the UK, increasing the economy as a flagship species.
Seal disturbance is a complicated issue. It can be anything that the seals are threatened by, such as unfamiliar smells or sounds. As mentioned already, hauling-out is extremely important for their life cycle - they haul-out to breed, moult, digest food and to restore energy levels.
Increased human activity results in disturbance, which can cause flushing- this prevents them from hauling-out. Flushing can also cause injuries to the seal's claws or skin from sharp rocks and marine litter.
Photo by The Seal Alliance
During pupping season, if disturbed the mothers may leave their pups alone leaving them vulnerable which is why so many baby seals end up in the animal hospital in the Cornish Seal Sanctuary. The mother may delay returning to feed her pup or even abandon her pup altogether, resulting in malnourished pups and reducing survival chances during their first winter which is a dangerous time for these little white fur balls.
Humans approaching too closely from shore or by boat can disturb pupping groups. Boats in the sea can distract foraging behaviour, particularly in juvenile seals who are still learning the ropes. They are often seen approaching boats, not seeing them as a danger, and boat operators feeding them.
In my study, I conducted a land-based survey at two different coastal sites in Cornwall.
A greater number of seals were seen at Site A (on average 20), whereas at Site B an average of only two grey seals was seen.
Seals displayed a flight response when boats approached within 200 m.
Over the total 8 weeks of observational surveys at both sites, 82% of boats witnessed, became a disturbance to the seals. High traffic of boats occurred when weather conditions were good. During this time, more boats were seen approaching the breeding site near Site A increasing the vulnerability of the seals.
Data obtained from my study helps understand the need to protect grey seals from human disturbance, and the different physical behaviours that are displayed in response.
Below is a bar chart showing the total number of each type of disturbance at each site, blue bars for site A, and green bars for site B.
My findings showed that increases in human disturbance do negatively affect the behaviour of the grey seal (Halichoerus grypus), increasing stress responses such as flushing, aggression, and often injury.
If you are interested in reading more about the disturbance of seals in Cornwall, a friend of mine runs the Cornwall Seal Group Research Trust!
One of her articles can be found at https://www.cornwallsealgroup.co.uk/wp-content/uploads/2019/07/2019-07-DO-NOT-DISTURB-public-report-for-release.pdf
Written by Darby Bonner