What does the other end of the spear look like? How long is the metal shaft overall? If it's a whaling spear, it should have a hollow socket where the handle inserts and it should be fairly long (18"+) overall
The pivoting fin below the point appears to be in line with spear tech of the time but the 2 screws make me think it's much later Usually the pivot point was offset so when it pierced flesh, the force of the whale pulling away would lock the spear in place, similar to broadhead arrows used by hunters today. Yours appears to just pivot evenly from side to side.
I'm by no means an expert on this stuff but I've been hunting for spears with my girlfriends mom in cape cod for years. We've talked to many "authorities" on the subject and I've leaned a great deal. I don't think I've ever seen a whaling spear/lance with hardware. All were forged and any pivots were set with pins.
It might be a spear for tuna or sailfish.