Manatee Facts: Manatees are herbivores that feed primarily on seagrass and macroalgae. Manatees are serious eaters. They can spend upwards of half of their day munching on vegetation, which results in daily consumption of plant matter matching 10% of their body weight! Manatees can hold their breath for up to 20 minutes, but most will come to the surface every 3 to 5 minutes to breathe Manatees can swim at speeds of 20 mph for small bursts. Manatees can live for 60 years or more.