This month should be prime pupping season on the spectacular Cornish coast, whose rich waters and sheltered coves attract grey and common seals from all around the British Isles and beyond. But wildlife groups are concerned that seal numbers appear to be lower than in previous years – and part of the reason is down to a rise in “silent” water sports.

Up and down the country there has been an alarming increase in incidents where humans, dogs or drones have caused disturbance to one of the UK’s most important wildlife populations. The number of recorded seal disturbances in Cornwall alone has doubled since last year, according to data collected by the Seal Research Trust. It believes that the huge growth in kayaking, paddleboarding and wild swimming is now a significant factor.

“Seals will hear a boat engine from a long way off,” said the trust’s founder and director, Sue Sayer, who is campaigning along with other wildlife groups for people to keep their distance. “But with paddleboards and kayaks, the seals may not wake up until there is someone really nearby. Then their panic response is greater because they are so close up – they feel threatened immediately and either tombstone or stampede into the water.”

Disturbance is classed as a change in an animal’s behaviour that causes harm to its health, wellbeing or survival. For seals, a disturbance is most damaging when they are on land, where they are less mobile and feel more vulnerable to threats. “A seal has gone on to land for a reason – to rest, to digest their food, to give birth, to moult. They will stay out for the whole low-tide cycle, and be washed back into the sea as the water rises. If a seal is disturbed by noise or people during that time, that causes a panic response,” said Sayer.

Panicked seals will stampede to get back to the water, often sustaining severe cuts on the rocks. Pregnant females can lose their unborn pups, and newborn pups can be separated from their mothers. Tombstoning into the water from a height can break jaws and ribs, which ultimately can be fatal. Seals also suffer cold-water shock in a similar way to humans.

The Seal Research Trust recorded 934 serious disturbance incidents in Cornwall between January and July 2021, compared to 410 in 2020, and 269 in the same months in 2011. These are incidents where seals have been recorded as returning to the water as a result of human sporting activity or people being too loud or too close on shore. In the Mount’s Bay area in south-west Cornwall, the rate of disturbances has almost doubled in just two years, with an incident taking place every 15 minutes in 2021, compared to every 27 minutes in 2019.

A common perception of seals as curious animals who like to engage with humans is part of the problem, with videos of seals hopping aboard paddleboards and “photobombing” selfies getting a huge number of views on social media.

“As a kayaker, or if you are out on your paddleboard, you might look at their behaviour and think the seal wants to play, but that’s not the seal’s internal response if they are on land,” said Sayer. “As soon as they see you, their fight or flight response has been activated – their heart rate will rise, their breathing rate will rise, and that uses up precious energy. In the wild, every calorie counts – so every calorie that’s wasted on getting away from humans could mean the difference between life or death for a seal.”

Females are pregnant through the summer and need to conserve as much body weight as possible in order to feed their pups and survive themselves after giving birth. Up to 60% of seal pups die within their first 18 months.

“One of the worst things people can do is try to feed seal pups,” said Dan Jarvis of the British Divers Marine Life Rescue, which has just opened a new seal hospital in Cornwall due to the increasing number of seals needing assistance in the area. Its first casualty was a two-week-old female grey seal pup rescued near St Agnes in late September, who weighed less than half the normal weight she should have been.

Jarvis is concerned that the climate crisis is also pushing seals and humans into greater contact. “Peak pupping season used to be October to November but now it’s becoming August and September, when visitor numbers to many coastal areas are at their highest,” he said.

The UK is home to more than a third of the world’s grey seal population, and seal campaigners are pushing for a change in the law to make it illegal to disturb or harass a seal, in the same way it is illegal for whales and dolphins. “There is a gap in protection at the moment,” said Jarvis.