The Gully is one of those descriptive local names, it refers to a deeper cut or trough in the bottom off Rhode Island and Block Island. Depressions like this are important structure: they funnel current and gather bait, and bluefin use the edges of the cut to ambush what the current brings.
The ground
Fish the edges and lips of the depression, where the bottom changes depth. Current moving across the cut concentrates sand eels, squid and other forage, and the tuna hold on the productive edge.
How to fish it
Troll the edges to find fish and jig the marks, paying attention to the depth changes on your sounder. The bait that stacks in the cut tells you what to match.
Tip Watch your sounder for the edges of the cut, that is where the fish are. Trolling straight across a depression is far less effective than working along its productive lip where bait and tuna concentrate.