A surprise nursery of one of the world鈥檚 most elusive whales has been spotted in photographs taken from planes.
Narwhals, the single-tusked whales of the Arctic that have been dubbed the 鈥渦nicorns of the sea鈥�, are classified as 鈥渘ear-threatened鈥� by the International Union for Conservation of Nature. But protecting these animals is hard, partly because we don鈥檛 know how many there are.
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The animals spend about 80 per cent of their time under the water鈥檚 surface, and more than half the year in deep offshore waters below dense pack ice during the dark Arctic winter.
But in summer, the narwhals move to coastal inlets, where they give birth, giving us a chance to count them. About every five years, Fisheries and Oceans Canada (DFO) uses aerial photographs taken from planes to assess the numbers of narwhals living in the Canadian Arctic 鈥� about three quarters of their global population.
By studying these photos, Bertrand Charry at McGill University in Montreal, Canada, and his colleagues have managed to systematically count the number of baby narwhals there for the first time, a crucial step towards understanding how stable this population is.
Aerial count
Charry worked with photographs from a 2013 DFO aerial survey of narwhals taken 300 metres above Eclipse Sound and Admiralty Inlet off the northern part of Baffin Island in the Canadian Arctic.
Zooming in, he used factors such as size, colour and proximity to their presumed mothers to discern which individuals were newborns.
Colour was a clue because newborns are white or a lighter grey than adults. Babies also typically stick within two body lengths of their mother, Charry says.
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He found a surprising difference in their distribution. Of an estimated 35,000 narwhals in Admiralty Inlet, Charry found that less than 0.05 per cent were newborns, whereas in a smaller population of around 10,000 narwhals in Eclipse Sound, newborns made up nearly 5 per cent of group.
This suggests Eclipse Sound could be an important narwhal calving and nursery habitat. Charry presented his results at the ArcticNet conference in Vancouver last month.
Noise pollution
The finding may help the DFO and Nunavut Wildlife Management Board to create effective catch limits for narwhals. The summer catch limit for 2015-16 is 217 narwhals for Eclipse Sound, and 216 for Admiralty Inlet. For the sake of sustaining the narwhal population, it may be a good idea to reduce the numbers caught in the nursery population at Eclipse Sound, to avoid affecting nursing mothers or their young.
Eclipse Sound happens to be on the shipping route of a new Baffinland iron-ore mine, and this shipping activity might also affect the newly identified nursery. The company shipped its first load from Milne Port on Eclipse Sound in August 2015, and is in the process of ramping up production.
The increased shipping traffic may increase the noise pollution in these relatively pristine waters.
This could be a problem because, like all whales, 鈥渘arwhals are a sound-centred species鈥�, says Valeria Vergara, who researches marine mammals at Vancouver Aquarium. 鈥淢others and calves are a critical sector of the population, and shipping noise could affect the ability of mothers to hear their calves,鈥� she says.
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Image credits: Top: Paul Nicklen/National Geographic/Getty; second and third images: Bertrand Charry/Bruce Head Narwhal Study/Courtesy of Baffinland Iron Mines Corporation
