The dolphins often made a particular flat-toned whistle when they rode the waves created by [the] boat, and it's tempting to speculate that the whistle is the equivalent of a child going "wheeee!".-- from Dolphins use contextual 'language', which reports a study by Liz Hawkins of Southern Cross University who has identified 186 different types of dolphin whistle.
[Some other notes about cetaceans worth a look can be found at: Of Humans, Oil, and Whales, while Nature has a neat video on ancient whale evolution]
P.S. 21 Dec: 'Japan drops humpback whale hunt'.