Some good eating right there. Congrats.
I've never heard of folks trying to spearfish halibut in Alaska. Frigid waters, often some strong currents too. However, it is common to harpoon them once they're brought to the surface. You want to rake the gills with a knife and bleed 'em out. If they're nearing 100 lbs. in size you hog-tie 'em. You catch a "barn door" (300 lbs range) and you don't have a big enough boat to know everyone remains safe, you drag them back to shore and do not even try to bring them into the boat, too dangerous. Even after bleeding them out and you know they're dead, even 45 minutes later they can begin thrashing, that's why you hog-tie bigger ones. Be prepared once you get them to the boat, as soon as their nose leaves the water they'll go ballistic.Bucket list items for me!
1. Go visit Alaska
2. Try and catch a 'barndoor'. I still cannot believe people spearfish those things!