We could mention the 1969 novel "The Day of a Dolphin", by Robert Merle ("A Sentient Animal" or "Un animal doue de raison"), adapted loosely into a movie in 1973 with George C. Scott, about a dolphin who, after training, is kidnapped and used in an assassination plot. I read the translated boo when in the Army.
Update: June 15, 2015
The June 2015 issue of National Geographic has a followup article on p. 58, "Born to Be Wild", by Tim Zimmermann, said to be the second of a three-part series "Understanding Dolphins", "Captivity", showing programs to release them back into the wold.
Update: July 20 2016
The July 2015 issue has part 3 on p. 80, "Feeding Frenzy", by Virginia Morell, explaining how matriarchal pods of orcas hunt for "free fish", train the young, and engage in "carousel feeding", even forcing sea lions to beach.