This setting is already built into the fishing spot (Fishing Zone Device).
Look for the setting Pool Type (red arrow), in the drop down menu you can set it to use the default battle royale weapon pool, or use your own custom weapon pool.
to use a custom weapon pool, set the Pool Type to Device Inventory, then in the Item List (red circle) you can add the loot you want.
There is also a setting in the drop down for Fish Only so you cant catch any weapons, just fish.
And there is another setting called Trigger Only where you will not catch anything, but send a trigger. So you could trigger an item granter to give the player a specific weapon, or random item(s) you choose, or nothing at all.
hope that helps
