Endurance

Ryan Keene and his sea lion, Hansel, are members of the US Navy's Marine Mammal Program, which sounds exciting but rarely involves any real danger. Mostly they are responsible for recovering lost objects from the ocean floor. That all changes they travel to the perilous Arctic, where polar bears stalk the ice and killer whales prowl the water. But even at the ends of the Earth, the most dangerous predator is man.