December 29, 2014 - MOTHER NATURE -
While hunting, Weddell seals have biological adaptations that allow them
to dive deep, as much as of hundreds of meters, but also an uncanny
ability to find the breathing holes they need on the surface of the ice.
Now, researchers supported by the U.S. National Science Foundation
(NSF) believe they have figured out they do it: by using the Earth's
magnetic field as a natural GPS.
"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.
If the hypothesis turns out to be true, it would represent the first evidence of such a trait in a marine mammal.
Highlights
of the research have been captured on video in underwater images and in
interviews by myself and Ralph Maestas, of the "Antarctic Sun"
newspaper, which is published by the U.S. Antarctic Program (USAP). (NSF
manages the USAP, which coordinates all U.S. research on the
southernmost continent.)
GPS as a matter of life and death
The
question of how seals navigate is more than academic. It's about life
and death for the animals, which like all mammals, 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.
"These animals are
doing a remarkable amount of exercise all while on breath hold," notes
Terrie Williams, a professor of ecology and evolutionary biology at the
University of California-Santa Cruz. She is an expert on physiology in
the Weddell seal, an animal whose apparent lethargy on the surface of
the sea ice belies an amazingly athleticism below it.
"The reason
a seal wants to be efficient is that they have a limited amount of
oxygen onboard," she explains. "The trick is conserving that 'scuba
tank' on a dive." [Images of Rescued Seals and Sea Lions]
Davis,
Williams, and another colleague, Lee Fuiman, associate director of the
University of Texas' Marine Science Institute in Port Aransas, have been
studying the behavior of Weddells for decades.
Tracking the dives
The
idea that Weddell seals can unerringly follow magnetic lines dates back
to the late 1990s when the team first started working together in
Antarctica. Fuiman said he was struck by data from the very beginning
that showed the seals returning to dive holes with amazing precision.
"The
animal always found its way back. It's like he knew exactly where the
hole was," Fuiman said. "I couldn't figure out how they would do that.
How did they know where they were by the time they turned around?"
The
behavior from the dive profiles is intriguing but not conclusive. So,
how would a scientist determine whether Weddell seals, like homing
pigeons, are using magnetic lines to weave their way back home?
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.
"There should be changes in behavior when an animal is in a different magnetic field," Fuiman explained.
In
other words, comparing the magnetic anomaly maps of McMurdo Sound with
dive profiles from the video and data recorder should provide some
answers.
"That will give us the amount of data that we need to
statistically analyze the information to look for these hypothesized
behaviors," Davis said.
Or is it something else?
Next
year, the group will return to Antarctica in August toward the end of
the Antarctic winter, when there are still 24 hours of darkness. Davis
said it's possible Weddells may be using other strategies for relocating
holes in the sea ice with apparent ease. One possible explanation
involves the idea of piloting using under-ice visual features, such as
cracks in the ice, to navigate.
However, without light penetrating the ice during winter darkness, the team can eliminate another factor.
"Magnetic
sense isn't the only sense that seals use for orientation," Davis said.
"What we're trying to do is separate pilotage from navigation."
Another
sense that may be in place is hearing. Seals may be receiving acoustic
cues from other Weddells on where breathing holes are located. In that
case, Davis explained the team is using a directional hydrophone to
pinpoint the direction of vocalization.
"Being able to travel
reliably between sparsely located breathing holes is absolutely critical
for their ability to live under this ice," Davis said. "We're trying to
take away as many other potential orientation abilities of this animal
and focus on this one aspect, which is the magnetic orientation." -
FOX News.
