Alaska wildlife management says that the minimum rifle for all alaskan wildlife is a 308
I just looked at the alaskan huntingregulations at the link below and I could not find a regulation specifying the minumum caliber for big gameas .308".In fact they do specify that you can use a .22 rimfire to take swimming caribou in two management units.
http://www.wildlife.alaska.gov/regulations/pdfs/general.pdf
How about posting the link where you found that information.