Spotting seals in a rapidly changing Arctic with your eyes on the sky

This summer, researchers managed to collect stunning drone images of ringed seals and walruses. In one fjord, St. Jonsfjorden, twelve ringed seals were found scattered throughout the fjord, resting on the fast ice. However, addressing and identifying these individuals is very difficult. Since ringed seals are preyed upon by polar bears, any mammal – four-legged or two-legged – is avoided at all costs.

“By using a drone, we managed to capture high-resolution images of ringed seals on the ice, resting next to their breathing holes. The species can be easily identified from these images,” says Geert Aarts, project leader of the Arctic Seal project. The researchers also obtained Maxar satellite imagery for this particular region.

Since the ice is confined and does not move, the locations of the breathing holes are virtually fixed. The researchers were therefore able to directly match the individual seals that were on the drone image to the breathing holes visible on the satellite images. “Although aware of the potential of such satellite imagery for observing mammals from space, we were surprised when we noticed white lines across the ice sheet connecting ringed seal spiracles. In this remote and hostile environment, this can only mean one thing: polar bear tracks.”

Machine learning to count arctic mammals

The resolution of satellite imagery has improved significantly over the past decade. These satellites, orbiting the earth at an altitude of more than 600 km, can photograph any location on the earth’s surface with a resolution of 30 x 30 cm. By also downscaling the high-quality drone images to a resolution of 30 x 30 cm, the researchers can create a photo that mimics that of the satellite images taken from space.

“Ultimately, these images can then be fed into a machine learning algorithm and used to train a neural network,” says Jeroen Hoekendijk, Ph.D. Candidate who was part of the research team and works together with the EPFL to further develop these techniques. By applying this trained network to satellite imagery, the researchers hope to be able to automatically detect seals in these remote and hostile regions.

Seal species use the polar ice differently

Seals and walruses are particularly plentiful in the arctic regions. Each of these fin species has its own unique characteristics and relationship to sea ice.

Ringed seals, for example, bore breathing holes in sea ice attached to the shore. These breathing tubes can be several meters long and connect the seawater beneath the ice with the air above. By using their claws on their front flippers, they prevent these breathing holes from freezing over. During the long and dark winter months, these breathing holes are covered with snow. These snow caves offer their pups some protection from the harsh conditions outside.

Harp seals, on the other hand, rest and give birth on the drifting pack ice. This pack ice covers most of the North Pole region in winter and connects all landmasses in the polar region, but shrinks in the summer months. Unlike fast ice, pack ice drifts and can move several kilometers per day.

Sudden changes in current and wind direction can quickly lead to a collapse of the harp seal’s birthing platform. Walruses also use the pack ice, but individual animals also rest on land. During the research expedition to Svalbard this summer, researchers also managed to collect drone images of walruses that could help others develop similar machine learning techniques for this species.

Change home quickly

Ultimately, researchers hope to use these remote sensing techniques to locate seals in the Arctic. Your home is changing rapidly due to climate change. This applies in particular to the northern Barents Sea and the islands of Spitsbergen and Franz Josef Land.

This region is the fastest warming place on earth, with average temperatures rising by 2.7°C per decade and as much as 4°C per decade in the autumn months. Therefore, there is an urgent need to know which habitats seals rely on in order to study the effects of climate change and to conserve these species.

Provided by the Royal Netherlands Institute for Marine Research