The Blue Machine

These whales feed on fish, and those fish are much less salty than the ocean. As they’re digested, their carbohydrate and fat release water, and the fish themselves contain useful water in their cells. So if a whale is careful, squeezing out the seawater that comes with each mouthful of fish before it swallows, it can get enough water from its food without taking in too much extra salt. We don’t yet know for certain, but it seems likely that whales don’t need to drink. 33 The work of eliminating excess salt is largely done for them by their fishy prey, who are experts at drinking seawater and then pushing salt back out into the environment though their gills, urine and faeces. Few ocean vertebrates drink, but all of them face the challenge of keeping the water in and the salt out.