In deep water they are probably trying to release air from their swim bladder to adjust their buoyancy.
Or maybe they just feel froggy.
A lot of different species breach in order to gulp air where oxygen levels are low. They may also be trying to knock parasites off.
Edited by Muzzlebrake (09/06/17 08:57 AM)
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."
Then He made the earth round...and He laughed and laughed and laughed!