Monk seals have found an unusual way to hide from tourists

Scientists observed seals near the uninhabited island of Formicula, a popular place for boat trips, swimming and meetings with marine animals. It turned out that in high season, seals regularly use not only the usual sea caves, but also so-called bubble caves - moist underwater cavities with air inside. The study is published in the journal Oryx.

Important: seals do not "hide from tourists" in the human sense. It's about reacting to disturbance. When people swim too close, enter caves or try to interact with the animals, the seals may change behaviour and retreat to more inaccessible resting places.

Details

The Mediterranean monk seal (Monachus monachus) is one of the rarest seal species. Historically, these animals rested on open beaches, drying their fur, giving birth to their calves and raising them on the shore. But because of human pressures - past hunting, coastal development, tourism and constant disturbance - they are increasingly using remote sea caves.

Formicula is located in the Inner Ionian Archipelago. It is a small uninhabited island with clear water that attracts tourists. At the same time, it is part of an area important for resting, feeding and breeding of monk seals. Conservation material on Formicula specifically emphasises that uncontrolled human presence can prevent animals from using key habitats.

To understand exactly where the seals go, the researchers installed automatic cameras. One was placed in the main cave, where the animals had been seen before. The other was placed in a waterproof enclosure at the entrance to the neighbouring "bubble" cave.

This is the name for an air chamber or dome that can only be accessed underwater. Inside, there is no dry beach or rocky area where the seal can get out of the water. But there is air in there, so the animal can stay in the water and breathe by surfacing inside the hidden cavity.

The observations were conducted for a total of 141 days: first a short period in July 2020, then a longer stretch from June to October 2021. The result was notable: seals were recorded in the 'bubble' cave for 119 days, but only 30 days in the main cave.

Inside such caves, the seals didn't just linger for short periods of time. Cameras recorded them resting near the surface, sleeping upright in the water or lying motionless on the seabed. This shows that underwater air domes can be full-fledged resting places for them, rather than occasional stops.

Why it matters

For a rare species, a resting place is no small thing. If an animal is constantly disturbed, it may expend more energy, avoid familiar areas, rest worse and use suitable breeding sites less often. For a small population, this is especially dangerous.

The discovery is also important for conservation. If such underwater air chambers do indeed serve as refuges for seals, they should be taken into account when planning protection zones. Only visible caves with a beach inside cannot be protected - some of the important sites may be hidden underwater and outwardly almost invisible.

The researchers explicitly note that assessments of suitable habitats for the Mediterranean monk seal are worth supplementing with such 'bubble' caves, especially in areas with high tourism pressure.

Backcountry

Mediterranean monk seals have been retreating from open areas to more hidden locations for centuries. They used to use beaches more often, but now many populations depend on hard-to-reach sea caves. This helps the animals avoid humans, but creates new risks: suitable caves are scarce, and tourist boats and swimmers are increasingly reaching even remote sites.

Formicula is one of the few areas where seals can be seen regularly. This is why the place attracts tourists, but for the same reason it requires strict management. Conservation organisations have already sought restrictions to protect the area; in 2026 it was reported that the new measures should help the seals rest, feed and breed without disturbance during the summer months.

This story illustrates well the conflict between "ecotourism" and real conservation. The desire to see a rare animal can itself become a threat if people swim too close, enter caves or disturb the animals.

Source

Joan Gonzalvo et al, "Sealed serenity: use of underwater bubble caves as refuge against disturbance by Mediterranean monk seals", Oryx, 2026. DOI: 10.1017/S0030605325102718. The article was published online by Cambridge University Press on 28 April 2026.

In the study, scientists used remote cameras to monitor Mediterranean monk seals off the islet of Formicula in Greece. Over 141 days of monitoring, the seals used an underwater air dome cave significantly more often than the main cave. The authors believe that such hidden chambers may serve as important resting places and refuges from human disturbance.