Grab your salvage hooks, if you get your boat close enough to the NPC and buy all 500 you can move a step and use your rope line to hop on to the boat and all 500 anchors will drop on to your boat instead of the ground (requires one of those new boats) it just requires good timing and some practice (Anchors weigh 25 stones each, test with like 20 at a time.. Not like me who tested with 500 at a time and got lucky the first two times and not so lucky three times after...), then take your boat to deep sea within guardzone and start hurling the hooks overboard. When the monsters spawn you can guardwhack them. Another note: you don't need to even kill the the monsters for a chance at the fishing pole, you can slow forward and troll the sea.
I've gotten 5 poles using both of these methods, sold 2 poles for 35m each :>
Some aftermath screenshots
Trolling:
