Continuity mistake: The sky at the end changes several times from being cloudy to clear. Look at the reflection of it when Willy comes over to Jessie in the water. The next shot is cloudy. The jump scene is clear, and then it is sunny.
Continuity mistake: At the beginning when Willy is captured, the sky changes dozens of times. It goes from being overcast to sunny to cloudy.
Answer: While sounds and words can be used to alert orcas and dolphins, they recognize the hand signals and movements as to what to do.
LorgSkyegon