A similar story: my brother was bottom fishing with some guys at the South end of Revillagigedo Channel (near Ketchikan). Three of them caught lots of fish, one hardly any, until he did. They fought it for an hour or more taking turns, into dark thirty. When the halibut finally started coming up, Jerry (my bro) was leaning over the side, ready to gaff it. When it came into view he said it was like a truck coming at him. Their boat was already pretty full of fish, so somehow they managed to tow the halibut slowly back to the NOAA (mother) ship coming in way late, and they winched it aboard. If I recall correctly they estimated it as well over 300#. And then the ships crew saw all the fish in the boat. “Where in the hell were you?!!”
That was in the late 70s.