The mysterious lifestyle of Greenland sharks makes them incredibly difficult to follow. Peter Bushnell and John Steffensen have been studying these animals since 2011 and it was only recently that they found a way to track them. On their latest expedition they employed a new tagging method that provides ground-breaking insights into not only where, but also how deep Greenland sharks go.

How do you track a shark that lives in the depths, often beneath ice floes, in the northernmost reaches of the planet where the sun glares for weeks in summer but doesn’t emerge at all in winter? SPOT tags, which rely on GPS, work perfectly for animals like white sharks that come to the surface; PSAT tags, which estimate geographic position by measuring depth, time of day and light intensity, are effective at locations closer to the equator. Neither, however, is suitable for Greenland sharks. Since beginning his research, Bushnell has tagged 20 Greenland sharks, but the only locations he has been able to pinpoint were the exact sites where the PSATs were deployed and where they popped up after three to nine months. To discover where the sharks go and whether populations on the eastern and western sides of Greenland are mixing, he needs more detailed information about their movements.