It could have been a giant skate. I had one do about the same thing last year out of Westport. Unlike a halibut, their mouth is on the bottom side of their body so even if you could get them to roll over, it’s still like bringing up a barn door because they come up flat. We estimated the one I had to be well over 80 pounds. They don’t shake their head because they don’t really have one but the surface area of their wings is huge so just a little bit of wing flutter creates a whole lot of power and movement. I thought I had kelp with rocks in it, until it took off then I thought it was a halibut. I didn’t think I would ever get it to turn. I was mooching with a medium action graphite salmon rod with 50# Power Pro and 30# leader; I broke the rod off right above the first guide. I was really pi$$ed when I realized I broke a good pole for a junk fish. We got it up to the boat and looked at it for awhile and took some pictures then I retrieved the other half of my rod and then cut the line and it kind meandered off.