If you just want meat, then get a karve more desirably or long boat, find a serpent, and then set the boat to slowly turn on a sail and shoot the serpent. If you're pure melee or need scales, then bait them nearish land just before they lose aggro, harpoon them with lot a large stam bar (good stam food) and then start whacking away. If it's slipping back then you could build a workbench and some walls to block it off.