Dolphins communicate using compression waves (longitudinal waves). some of the sounds dolphins make are outside the range of human hearing. upon spotting a hungry shark, dolphin a sends a message to dolphin b. to send this message as effectively as possible, dolphin a would question options: send the message above the water when it jumps because air is more dense than water, and the sound would be louder above the water. make a higher pitched signal because a higher pitch is a louder sound. make a softer sound because the shark will not hear the softer signal. send the message underwater because a more dense medium produces a louder and faster sound.