As reheat suggested don't forget the cargo....
As well as 400-500 passengers, the ferry also carries 110 cars, if I've got it right. Sounds a bit like the X-Channel hi-speed ferries between the UK and France. If we assume that they would be transported by sea in any event (not necessarily so, but quite likely) your comparative sums would start to look a bit different.
But on the other hand, there's the whales to think about; I imagine a ferry would give one a nasty headache, if it didn't hear it coming and dive in time. The whale, I mean, not the ferry. That is, if the whale didn't hear the ferry and dive, not if the ferry didn't hear the whale and dive...Oh God how did I get into this.......heeeeelp....