Hey Bow,
Welcome aboard and here is a cut and paste straight from the WDFW Regulation Site:
LANDING A FISH - A club or dipnet (landing net)
may be used to assist landing a legal fish taken
by legal gear. A gaff may only be used to land a
legally hooked HALIBUT, TUNA, or DOGFISH
SHARK that will be retained. HALIBUT may be
shot or harpooned while landing.
I would certainly keep a gaff on board because as Robbo correctly pointed out (as much as that pains me to admit...

) most of your Straits of Juan de Fuca 'but's can easily be handled by a gaff.
A good question to ask is "how big must a halibut be to put down the gaff and pick up the 'poon?"
I put that line at 75 or 80lbs which is about a 55" halibut. Once they get to be five feet tall, you've gotta swing 'em over the gunnel with some momentum.
Keep in mind that once the harpoon goes through and sticks, don't wait for the halibut to make the next move. Have your fishin' buddy put the rod down, pick up the gaff, slam it home and yard that beast into the boat!
You can high-five and plan the fish fry AFTER you get your gear back down! You're not limited yet!
