The barge guard guards the Digsite barge. Additionally, the guard is the way to travel to and from Fossil Island upon completing the quest.
Boarding will place you on the ship accompanied by the guard, the Junior Navigator and the Lead Navigator. You are unable to travel to the island by speaking with the guard; however, if you wish to deboard, there is an option to do so. When boarding, the in-game message "The barge guard helps you board the ship." appears. When you deboard, the in-game message "The barge guard helps you off the ship." appears.
Quick-traveling takes you directly to Fossil Island without having to get on the ship.