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

Randall Davis of the Department of Marine Biology at Texas A&M University, Terrie Williams, a professor of ecology and evolutionary biology at the University of California, Santa Cruz and another colleague, Lee Fuiman, associate director of the University of Texas' Marine Science Institute in Port Aransas, have been studying the behavior of Weddell's for decades. The idea that Weddell seals can an 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.

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

Randall Davis of the Department of Marine Biology at Texas A&M University.

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.

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."