NORTHCOM’s on line magazine “The Watch” reports,
“TThe USS St. Louis returned to its home port of Mayport, Florida, on November 10 following a surge deployment in support of the United States Coast Guard’s maritime interdiction mission. The U.S. Navy Freedom-variant littoral combat ship, which carried a Navy helicopter and embedded U.S. Coast Guard law enforcement detachment (LEDET), patrolled U.S. waters near the southern border with Mexico, under the direction of the U.S. Northern Command (USNORTHCOM).
This was an unusual deployment. Normally US Navy ships supporting Coast Guard interdiction efforts operate under SOUTHCOM, specifically under Joint Interagency Task Force South.
No interdictions were reported.
Chuck Hill's CG Blog 
I would imagine their operations were in the Gulf supporting anti-cartel operations coordinated with the border activities North/South. Special Operations I would think would be involved.
The report says it was near the US / Mexican border so yes in the Gulf. Apparently caught no immigrants or drug smugglers.