A Quiet Place Universe

In the film A Quiet Place, the world has become overrun by huge, bulletproof aliens that can run extremely fast and hear a sound for miles around. In the film's lore, they spread throughout the world after landing in Mexico on an asteroid and conquered the Earth.

My question is, what happens to island nations in this univerise? For instance, the Caribbean, Great Britain and Australia. We know that the aliens can swim, as one is seen swimming momentarily in a flooded basement, although that's not the same as a 20 mile potentially rough crossing in the English Channel. Would there pockets of population on the world's islands or would they be doomed too?
 
Something that came to mind is that sound actually go longer distances underwater, hence why sonar and radar are effective.
 
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