The Coast Guard said Tuesday it was suspending the search for a University of Southern Mississippi student missing since Sunday in the Gulf of Mexico off the Alabama coast.

Crews searched nearly 1,800 square miles without finding any sign of Robert Brent, 20, of Yazoo County, Mississippi. He was last seen while swimming off the southern shore of Dauphin Island, and a friend reported him missing after he disappeared from sight.

The U.S. Coast Guard joined local authorities in a search, which has included aircraft, boats and teams combing the shore.

“Unfortunately we have not been able to locate this young man, who was loved by his family and community. Our deepest sympathies are with the family right now,” Lt. Cmdr. Erica Brewton, who coordinated the search Coast Guard Sector Mobile, said in a statement.

Southern Mississippi, located in Hattiesburg, issued a statement saying it is saddened by Brent’s disappearance and is offering support to his family and friends.