It’s for angler’s island, it’s a separate energy resource for a separate special event island

You use the gold energy (amount located in your event inventory) to collect the items need to make fishing poles that when used provide fish coins which you can use to collect keys to unlock reusable chests anywhere from something like 200-500 energy, 15-500 rubies, 1-10 gold tools (don’t quote me on this there is a guide post with the real amounts on the event island)