This is one of the reasons I love hanging around certain RPG forums; every other day I learn something new.
My reaction was: "What kind of idiot shoots fish in the brain?", but a 5 sec search on google showed me what a halibut is. Yeah, I can see how you could need a fast-killing method when the fish in question can weigh several hundred kilos and be larger than you.
It's not that the fish is a threat to the person; it's that a live halibut is a threat to the BOAT.
A 250# halibut (about 120kg) TOWED a 40' boat. Over a mile (1.6km).
A typical halibut sport-fishing "experience" is get on a boat, sit aroud for 30-60 min.
Then, everyone baits their end tackle. Everyone drops lines. Either very quickly everyone's catching, or no one's catching. in the latter case, another 10-20 minutes under way, and repeat.
Once people have them on, lever up, reel down, repeat. Smaller halibut (50-120#; 20-50kg), get brought up, and on a good school, the skipper literally will walk around the boat shooting any that appear to be over 50#. Bigger ones instead get harpooned, and tied to the prow.
When the big ones are harpooned, they usually take off... and drag the boat.once they slow down from exhaustion, drag them up and shoot them, then everyone works to get them aboard. Crew and passengers alike.
Smaller ones, 50-80# (20-65kg) might be brough aboard and beaten with an oosic or a fishbat (natural or manmade truncheons); bigger ones would be harpooned, tied off, allowed to run, and when tired out, beaten with the oosic. Walrus and beluga whale oosic is the typical aboriginal tool for the job.
Under 50#, typically, they get thrown back.
Once everyone's got limit, 30-90 min back to port, followed by a cleaning frenzy.