The governor of Alaska issued Administrative Order No. 321 on 4/26/2021. This order prohibits entities under the Alaska Executive Branch from requiring anyone to produce their personal vaccine history for the purpose of traveling to or around Alaska.
The order states that the Alaska Marine Highway ferry system may allow passengers to voluntarily show proof of COVID-19 vaccination in order to avoid a requirement for a negative test prior to boarding.
https://gov.alaska.gov/admin-orders/administrative-order-no-321/ - text of the administrative order.