My sister in law took the sea otter quest with her 3 girls. They loved it. They got to see a bunch of otters and whales and other wildlife. But they booked through the ship, so I can't offer any local tour guides that you could book yourself. Try the internet, google on Sitka and tours and see what you get.
As far as other things, we found a little sea "petting" zoo. If you walk down to the end of the docking area (you tender into Stika) and turn right at the main harbor side street, you will see a city park with tennis courts etc... If you go down a little past the tennis courts, there is an Aquarium. They let you pick up and or touch various reef creatures (Star fish, sea cucumbers etc...) and they have some aquarium fish. It was a cool experience for our 11 year old and it was free (they asked for a donation, but didn't ask for any particular amount.) If you have a yound one, it is a good idea.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013