No
Dolphins communicate under water by using echolocation
Whales and dolphins can't communicate under water
dolphin because it knows e = mc2
NO, they play with other dolphins.
Spotted dolphins can hold there breath under water for 7 to 8 minutes
Yes
They sleep under water.
If you mean, "are all under water creatures, sea creatures?" then no. The term SEA is for the ocean and there also can be creatures in freshwater. Also some creatures that live in water such as some snakes and sea turtles come out of the water every so often, so they are no total sea/water creatures. Fish are underwater creatures though.
Dolphins don t breath under water. Mammals breath air. Every 15 min they go out of the water to breath
yes
sonar
Yes they do but they do it under the water. Because dolphins need the same privacy as our humans.