Here's a link to the NPS guide. All of the white moorings on the north shore are managed by the NPS. There is a box with a slot at the mooring station to drop your $15 per night payment. The person who came around is the park host, a person who stays free on a mooring for a month in exchange for greeting and explaining the program. There is a box on the mooring station that has extra pay envelopes. You need to write down your mooring number and boat name on the envelope.

http://www.nps.gov/viis/planyourvisit/upload/MooringGuide.pdf

Cheers, RickG