User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5460283-20130102043847/@comment-4212769-20130103181754

Another reason why the eggs cannot survive in great depths is the pressure. The size is significant in this. A small egg is a lot more stable and has to deal with less pressure as the area is crucial for this. A bigger egg is less stable and has to deal with more pressure so there's a limit of size. Ceadeus eggs for sure surpass this limit.

Also that he can be at the surface, that's kinda obvious as he cannot breathe underwater. lol But how should he get the egg to stay at the surface? Also 1-3 miles is a lot pressure that could surely break the egg..

And it doesn't trap oxygen. Three problems: 1. We don't see bubbles/bladders that contain oxygen in the beard. 2. When the beard is cut it would drown if it would rely on it. 3. The most important: How should it get it into its lungs? It doesn't have access to put the air from the beard to the mouth to breathe it in.