Climate-vulnerable winter feeding of narwhals is essential for survival: study

PARIS — Narwhals are likely more dependent on fat reserves and plentiful prey in climate-challenged winter habitats than previously thought, researchers said Wednesday, warning of serious risks from global warming.

Scientists studying the long-horned marine mammals in the fjords off the east coast of Greenland over the summer found that narwhals were largely unsuccessful at capturing prey.

“(This) suggests that they may actually rely on the wintering grounds to build up sufficient body reserves and energy stores to sustain activities year-round,” said Philippine Chambault of the University of California Santa Cruz, co-author of the in study published in the journal Biology Letters.

Researchers believe most narwhals spend their winters feasting on fish and squid beneath the sea ice off the coast of Greenland, but Chambault said this cold-water habitat could essentially “disappear” due to climate change, with expected rises in sea temperatures melting ice and possibly driving prey to move.

While the exact causes of the low summer feeding rate are not yet clear, the researchers could say it could be due to a decline or translocation of squid and cod, lower energy requirements, or even because they are picky eaters.

Normally, narwhals’ eating habits are difficult to track as they dive up to a kilometer deep and stay in open water.

Researchers were able to study the foraging behavior of 14 narwhals using so-called stomach temperature pills, which could detect when the whales swallowed cold prey and icy water.

They also used acoustic markers tuned to the sound waves or “buzz” emitted when narwhals approached their prey.

– ‘Little flexibility’ –

More than two-thirds of hunt dives recorded over approximately 1,000 hours were classified as unsuccessful due to the presence of buzzes without an accompanying drop in stomach temperature, the study found.

The researchers said the small sample size and the limitations of the equipment’s detection capabilities meant that feeding rates could be underestimated.

But they also worked with local indigenous Inuit communities to test their findings.

Inuit hunters examined the stomach contents of narwhals caught during the summer hunting season and confirmed that the whales’ stomachs were indeed “rather empty,” Chambault told AFP.

Food restriction is just one factor making the species’ survival difficult.

Their preference for cold water and a strong tendency to stay within or near their birthplace make them particularly vulnerable to climate change.

This means they “show very little flexibility to changing habitats,” Chambault said.