Gregg 'groggy' herring's ring is an item obtainable while Deep Sea Fishing. Upon catching this item a tool-tip will appear stating While fishing you find something unexpected. It can be taken to Gregg 'Groggy' Herring in the crow's nest at the top of the tall mast on the Deep Sea Fishing hub (2-storey building with nets). He is above the Fish Flingers' Fisherman on the upper level. You can't get up there - shout at him.
This completes the achievement My precious!.