Narwhals wield sonic ‘spotlight’

It’s not just their tusk that bursts straight from their head. Narwhals can direct their echolocation sonar beam like a spotlight, new recordings show.

Jens Koblitz from the Bioacoustics Network in Germany and colleagues from Europe and the US used underwater microphones to discover that narwhals are able to direct their clicks in a very precise forward direction – the most focused of any species to date.

The study, published in PLOS One, obtained some of the first ever recordings of narwhals in the pack ice of Baffin Bay, West Greenland, where more than 80% of the world’s narwhal population spends the winter – but are likely to be affected by human intrusion sooner rather than later.

“[The study] tells us really critical information about a species that we don’t know a lot about, but that is clearly going to be impacted by increasing human presence in the Arctic,” says Ari Friedlaender, an ecologist at Oregon State University in the US, who was not involved with the work.

Narwhals (Monodon monoceros) are considered one of the Arctic’s most sensitive marine mammals.

As Arctic sea ice shrinks in summer – some estimates predict summer sea ice will disappear altogether by the middle of this century – it’s expected their habitats will be criss-crossed by noisy ships.

This is a problem because like other toothed and beaked whales, called cetaceans, narwhals rely on hearing to hunt and navigate. They send clicking sounds and listen for reflections – this is called echolocation.

Understanding how these noises will affect the animals could give biologists an idea of how they’ll cope – or not – with a noisier environment.

So in 2013, Koblitz and his crew dunked microphones between three and 18 metres below the surface at 11 sites in Baffin Bay.

They found narwhal clicks were highly directional – like a spotlight rather than a floodlight.

Narwhals spend a lot of time in deep water, and an intense, forward directed sonar beam lets them detect prey far into the depths. The directionality also reduces confusing echoes from the water’s surface and ice above.

While narwhals are picky in their choice of habitat and extremely well-adapted to it, this makes them susceptible to environmental changes.

Knowing this, and that the Arctic environment is changing rapidly, Koblitz and colleagues believe that this is “a crucial time to obtain a good understanding of the baseline ecological and behavioural relationships between Arctic cetaceans, their environment and how they use sound”.

And as humans flood in, the narwhals’ environment is expected to change dramatically – particularly in its soundscape. We’ve seen this already – a study earlier this year showed high-frequency sounds produced by ship propellers are within the same sonar range as orca clicks. 

One of the major issues of increased human presence, Friedlaender says, is what’s called “masking”. More noise means the animals struggle to process their own sounds.

The other issue is that ships are using various military and mapping sonars that might be in the hearing range of various cetaceans. These can cause the animals to stop feeding or move out of certain areas – disrupting their normal patterns.