Weddell seals may look round and ungainly on land, but these sleek creatures can swim up to 90 minutes without resurfacing for air - and this underwater longevity is helping scientists unlock the mysteries of the changing Antarctic.
The seals have the most southern range of any mammal, and they're also extremely docile, which allows scientists to glue tracking devices to their heads without stress on either party.
As the Southern Ocean warms, ice melts and the salinity and density of the water decreases. Thanks to the Weddell seals, scientists are beginning to understand what this might mean.
"They're really giving us a window into the Southern Ocean in winter in a way that we haven't been able to see before," said one scientist.