Listed on the wiki is that Sea Shanty with Epic Skill Focus Perform gives breathe underwater, this does not work. From my own experience and other bards.
Sea Shanty - Breathe Underwater
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Re: Sea Shanty - Breathe Underwater
This seems to have been fixed recently. Went to Benwick, and other bard said their song worked now. Tested and both our songs gave waterbreathing.