score:4
Poseidon is associated with dolphins. There are also stories of him having various sexual encounters with a large number of other humans and gods. These do include rapes and also transformations into other animals. However, I don't find an exact match for your line. I did however find that Melantho, Daughter of Deucalion, was raped by Neptune as a dolphin.
In Greek mythology, sex plays a big part. Many of the stories concern unpleasant aspects of sexuallity.