Can cetaceans breath through their mouths?

[Blind groper]

Dolphins and whales make their sound even when underwater with both mouth and blowhole closed. They do this by moving air back and forth internally. This is true for both communication and sonar sounds.

Since sound goes further and faster through water than air, sound can be used for long range communication and sensing. It has been suggested that whales use the sound of waves breaking on a beach hundreds of kilometres away for navigation. Humpback whales are known to emit communication sounds when the nearest other humpback is (as far as we can tell) dozens, if not hundreds of kilometres away.