Wow!
Yes , sounds and looks good for Pelagic to me, for all the reasons you give.
Don't see how it can possibly be Great or Temminck's, so yet another first.
Perhaps Mrs Davies did after all have the occasional "Resplendant Shag" (old name) on Cheung Chau in the 1930s! (see Chalmers 1986:249)
Mike Turnbull