My parents enjoyed their World Explorer cruise many years ago, just for the reasons you mention: naturalist onboard, no glitz, no focus on food/entertainment. It's not a small ship, but not one of the huge ones either.

A couple of my staff members went on Cruise West last May & came back raving about the experience. They sailed on the Sheltered Seas, which doesn't have accoms on board, so guests stay at port hotels for the overnights &cruise into all the little fjords &bays during the day. The cruise is quite intimate, with the focus on Alaska, not Las Vegas. Passengers range in age from young couples to retired, altho I would call them active retired. The photos of the glaciers, bays and wildlife they brought back were stunnning. The cruise is pricey, but it is the experience of Alaska that many people only dream about.

As you might surmise from past posts, I am not a cruise type (I went on one years ago &nearly threw myself over the stern by day 2; the only thing I liked was getting off for good on day 7), but this is a cruise experience I would consider.

Gail