There's three different types of irony:
situational irony- an unexpected twist occurs at the end of the story
verbal irony- sarcasm
dramatic irony- the reader knows something that one of the characters do not
I would say that the name "Ship-Trap Island" is dramatic irony because the reader can infer that the main character will be trapped on an island, but the main character has no idea that he will soon be trapped on the island and hunted.
