Just get the barb in him. Shot placement is not as critical as that on land critters. You really do not need heavy line to get him either. I use regular twine and when we haul him up from the depths (4 feet) we then jab a few more harpoon hooks under his hide. I like to shhot them as they swim away so the barb goes under the tough back hide but with that in mind the last two I shot both were in the head.