For scientists to solve the mysteries of the ocean, they need to start with questions like “how do fish float?” Duke University biology professor Sönke Johnsen joins host Krys Boyd to discuss the wonders of vertical migration, why sharks must keep swimming to stay alive, and the clues offered to biologists that help piece together the questions of aquatic life evolution. His book is “Into the Great Wide Ocean: Life in the Least Known Habitat on Earth.”