Feed the gulls
On the Otamoi cruise, you can buy bread and throw at the swooping gulls. It's a real delight especially if you share the ferry with young children who are so excited to feed the gulls.
On my trip, there was a funny bloke who stretched out to catch the gulls and actually succeeded in grabbing the wings of one of them. The gulls are very bold and will actually eat out of your hands.
The best scene is when a huge flock of them 'chase' after the ferry and when the ferry turns into port, they will all simultaneously take off in a parallel line - eliciting screams of "Sugoi" (excellent) from the locals. It's really amazing to witness the scene.

Bank of Japan Otaru Museum
Otaru Canal
Sushi
Lake toya