On Earth deep ocean creatures are adapted to a lack of sunlight, they're also not eligible to be crew members, since they're not intelligent.
Not intelligent? Dolphins serve in the Navy NOW. Veteran minesweeping dolphins are currently being interviewed for the National Archives about their experiences - seriously: interviewed. And the Indian government recently banned keeping Dolphins in captivity for shows, and issued this statement:
Whereas cetaceans in general are highly intelligent and sensitive, and various scientists who have researched dolphin behavior have suggested that the unusually high intelligence; as compared to other animals means that dolphins should be seen as ‘non-human persons’ and as such should have their own specific rights and is morally unacceptable to keep them captive for entertainment purpose.
Given more advanced tech and further research, I find it entirely possible that the "cetacean ops" section could be populated by alien and/or Terran cetaceans.
(Sorry if this seems overly defensive, but as far as I know, they aren't on TrekBBS yet
, so I felt the need to speak up for them.)