Don't know who told you you are required to keep everything you catch... They're wrong.
The only requirement to retain fish is that (in Southeast Alaska) you must retain all non-pelagic rockfish caught until your limit is reached.
As to other species, if you catch an undersized fish, or catch fish in excess of your bag/possession limit, you must release them. Few folks here will keep limits of chums or humpies unless keeping them for halibut bait, so most humpies and chums will get released. I tend to keep dime-bright saltwater caught chums for the smoker, but generally send every humpy we catch back into the water. There is no problem releasing halibut, but you cannot gaff a fish and then release it, so if you intend to release a fish either net it or pull the hook at the side of the boat.
There are pictures of the different salmon and rockfish species at the back of the regulations booklet, so be sure to pick one up when you buy your licenses. That way you will have pictures and regulations all in one neat package.
Enjoy your trip!
Chris
