It’s a sink or swim world. Ballast doesn’t just help to stabilize objects on the surface of water; it comes in awfully handy underwater as well. In this episode we listen in on the vertical migrations of plainfin midshipmen, follow local adventure seeking freedivers to talk buoyancy and where to stash your ballast, learn how buoyancy control strategies of fish and cuttlefish inspired a water-free ballast system for ships, and find out which creatures have developed a penchant for swallowing stones. Find show notes and a transcript at www.hakaimagazine.com/ballast-podcast.