How to count seals on drifting ice?

This winter, the adventure they have been looking forward to for five years was about to take place. Carefully planned, yet highly unpredictable. 

Icebreaker, helicopter, and a small plane are ready for take-off. But the researchers know all too well that weather, wind, and wave height could jeopardize the entire research plan. 

We are going to the West Ice, which is the drifting ice east of Greenland in the Greeland Sea, to count harp seals, and hopefully also hooded seals, on ice floes that are constantly moving. 

In search of blood 

The first thing scientists do, when the weather permits, is to fly back and forth across the ice in systematic east-west lines to locate ice floes with seals on. 

The expedition is carried out in March, during early breeding, and researchers are on the lookout for both seals and blood traces from births. 

"The weather has been on our side for the first few days, and we have covered the northernmost area, from the ice edge in the northeast at 75°N and all the way down to solid ice in the southwest, at 74°. As expected, there are not many seals to see so far north, but the area must nevertheless be covered so that we do not miss potential breeding areas," says expedition leader Martin Biuw. 

It is an exotic journey, and although there were not many observations of seals at first, there were other exciting experiences in sight. 

"We saw several groups of narwhales resting on the surface with their spears clearly visible, an event of rare occurrence," Biuw says.

Deserted, icy and exposed to weather

While the icebreaker RV Kronprins Haakon makes its way through dense drift ice south towards 73°N, the researchers on board are mapping the icy area. They scout for seals and breeding grounds, from helicopter and from the vessel. At the same time, another team is getting ready for take-off. 

In the far east of Greenland, a small plane has arrived from Norway, via Iceland. Two researchers from the IMR are getting ready to fly over desolate, icy and weather-beaten areas. 

"In this variable area, the weather can change quickly. A big challenge is that there is a long way between alternative airports, should conditions change while we are in the air. If we cannot land in Greenland, we must fly to Iceland, so the flight time must be constantly calculated so that the fuel reserves are sufficient," explains researcher Kjell Tormod Nilssen. 

The aircraft is first used to map whether there are breeding areas in the far south of the West Ice, all the way south to 70°N.

Red snow 

Closer to 72°N, the researchers on board Kronprins Haakon finally find signs of larger breeding areas. 

"There are dense patches of hooded seals, and clear signs of recent births. The otherwise snow-white ice is red coloured over large areas, and despite the helicopter's image, it's not hard to imagine the cacophony of howling seals beneath us”, Biuw says. 

Further south, an even larger breeding area for harp seals was located. 

"Despite the fact that we who are on board have all seen this scene play out before, it is always a sight that impresses”. 

There are seals everywhere, and especially along a 50 kilometer long strip of ice surrounded by more open water.

Perfect timing

There is a lot to work out regarding when the counting is to be carried out. The entire breeding area should be photographed with a camera that is fixed on the aircraft, preferably on the same day. 

Before the researchers get this far, they need to pay close attention to developments in the breeding areas. 

"Even though breeding of both harp and hooded seals is quite synchronous in time, all seal pups are not born on the same day, and it is important that the count occurs when as many seal pups have been born, but before the oldest pups are big enough to get into the water," Biuw explains. To find the perfect time to count, the helicopter flies at low altitude over the breeding areas, while the number of pups of different age groups is counted. 

"We do this 3–5 times with about 2–3 days in-between. Based on the age distribution of the young, we then choose the optimal day for counting. But there are several factors that must be correct on the big counting day," he continues.

Ice on the move

On the big counting day, the weather gods must play ball, with perfect flying weather. The entire breeding area is mapped, the time is set and it is ready for photography. But where exactly are the breeding areas now? 

The ice is constantly moving, ice floes are drifting with the ocean current and moving generally towards the southwest. 

But the researchers are well prepared and have marked several ice floes in the breeding areas with GPS transmitters. This allows them to keep track of how the ice floes drift and plan their flight route accordingly. 

"After a few days of strong northerly winds, the breeding areas have drifted with surprising speed towards the south-southwest. Without GPS, the job would have been almost impossible”, Biuw says.

Back home

Thanks to technology and the grace of the weather gods, the researchers were able to photograph the entire breeding area, both for harp and hooded seals in the West Ice, also this time. 

Both teams are safely back after the long journey, and now the researchers have months of image analysis ahead. 

"All seal pups in the pictures taken from the aircraft must be counted, and the result is used to calculate how many hooded and harp seals were born in the West Ice this year, and to estimate the size of the population. The results are the basis for IMR's advice on catch quotas on seals in the West Ice”.