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Antarctic seals may use Earth's magnetic field to navigate while hunting

A Weddell seal in Antarctica. Research indicates they may use the Earth's magnetic field to navigate. Photo: Peter Rejcek, NSF

Scientists believe they have found the reason that Weddell seals are so adept at finding breathing holes while hunting beneath Antarctica’s ice – they use the Earth’s magnetic field as a natural “GPS”.

If the hypothesis turns out to be true, it would represent the first evidence of such a trait in a marine mammal.

 

Skilful navigators

Weddell seals have biological adaptations that allow them to dive deep hundreds of meters deep while hunting, but scientists have been unable to explain their uncanny ability to find the breathing holes they need on the surface of the ice.

"This animal, we think, may be highly evolved with an ability to navigate using magnetic sense in order to find ice holes some distance apart and get back to them safely," explained Randall Davis of the Department of Marine Biology at Texas A&M University.

It's a matter of life and death for the mammals, which require oxygen to breathe despite their mostly aquatic environment. Time spent looking for a new place to surface after each dive would not only be inefficient given the energy required to swim and hunt, but failure to locate a hole in the ice means the animal would drown.

A team of researchers, from Texas A&M University and the University of Texas' Marine Science Institute in Port Aransas, have been studying the behaviour of Weddell seals for decades. The idea that the seals can unerringly follow magnetic lines dates back to the late 1990s, when the team first started working together in Antarctica, studying the seals’ diving profiles.

The behaviour from dive profiles is intriguing but not conclusive. So, how to determine whether Weddell seals, like homing pigeons, are using magnetic lines to weave their way back home?

 

Other possibilities

It's also possible that Weddell seals may be using other strategies for relocating holes in the sea ice with apparent ease, such as piloting – using visual features under the ice to navigate. However, without light penetrating the ice during winter darkness, the team doesn’t believe piloting could be the single contributing factor.

Another sense that may be in place is hearing. Seals may be receiving acoustic cues on where breathing holes are located from other Weddells. In that case, Davis explained the team is using a directional hydrophone to pinpoint the direction of vocalisation.

 

Further research

For the next three years, the team will work with a handful of Weddell seals. Each animal will be outfitted with a Video and Data Recorder and released into three areas over the course of a couple of weeks in McMurdo Sound, where researchers have precisely mapped the magnetic field.

In other words, comparing the magnetic anomaly maps of McMurdo Sound with dive profiles from the video and data recorder should provide some answers.

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