In the magical realism of The 23rd Letter, whales have learned how to talk, imitating human speech. This is not so far-fetched. See this news story.
The whales are the ones who are guardians of the sound of the 23rd letter. The Japanese fanatic Shiyama is trying to force them to make the sound for his own evil uses. They have refused, and he is torturing and killing them. Dexter’s psychic daughter Rachel has a special connection to the whales, and will come to their aid later in the story. The whales give artist Patrick McColley lots of opportunities for interesting visual panels in the graphic novel, like the moment when the whales are parachuted into the Mediterranean by the U.S. military!