Seals work harder to find food after sea-ice collapse

Scientists have made dire predictions about how Arctic animals will respond to sea-ice decline. Now changes are emerging that confirm what researchers feared. A new study shows that ringed seals in Norway are swimming farther, diving longer, and likely spending more energy to find food than they did before a major sea-ice collapse.

Ringed seals give birth, moult, and rest on sea ice. But in 2006, the sea ice near Svalbard, Norway collapsed, and the edge of the summer ice cap shrank north toward the Arctic Ocean Basin.

Researchers had already tracked 22 ringed seals in the area in a 2002-03 study. So the change in sea ice “created the possibility for a natural experiment exploring the impact of this dramatic environmental change on the behaviour of this species,” the authors of the new study write in Biology Letters.

The researchers attached data loggers to 38 seals and recorded their movements from 2010-12. Ten of the animals made offshore trips; nine seals from the 2002-03 study had done the same. From those 19 seals, the scientists collected data on about 30,000 kilometers of travel and more than 26,000 dives.

The seals spent roughly the same amount of time on their trips before and after the sea-ice collapse, the team reports. But in the latter group, the animals had to swim about 1 degree of latitude farther to reach the ice. Their average distance from the coast was 132 kilometers, while those monitored in 2002-03 were an average of only 67 kilometers away.

Once they reached the ice, the seals dove deeper, rested less, and travelled farther per day in 2010-12. For instance, they swam 44 kilometers per day and dove 36 meters deep, on average, over the Arctic Ocean Basin. In 2002-03, the seals swam only 34 kilometers per day and dove 22 meters deep on average in that area.

The results show that “past predictions… regarding climate change impacts on ringed seals were correct,” the researchers write. Ringed seals play an important role in the food web and are a major source of food for polar bears. Now scientists need to find out how changes in the seals’ foraging behavior will affect their population — and the animals that depend on them. Roberta Kwok | 19 November 2015

Source: Hamilton, C.D. et al. 2015. Predictions replaced by facts: a keystone species’ behavioural responses to declining arctic sea-ice. Biology Letters doi: 10.1098/rsbl.2015.0803.

Image © NOAA Fisheries