The first thing I thought of when I read about the harness-wearing, possibly Russian military trained, beluga found by Norway fishermen was Day of the Dolphin. Per Wikipedia:  The Day of the Dolphin is a 1967 science fiction thriller novel by French novelist Robert Merle. The plot concerns dolphins that are trained to communicate with humans, and their use in warfare. The central character is a government scientist with similar ideas to those of John C. Lilly.   It was also a good movie with George  C. Scott.