Atlantic City casinos continue to win less from gamblers. 

Tom Grill, Getty Images

The city's 11 gambling halls brought in $221 million in March, down 7 percent from the same month last year.

In March 2013, though, the city had 12 casinos. The Atlantic Club shut its doors for good earlier this year.

"If there's a difference in the number of stores, you can't really make comparisons that are meaningful," said Dr. Israel Posner, executive director of the Lloyd D. Levenson Institute of Gaming, Hospitality & Tourism at Stockton College.

Year-over-year revenues dropped a modest 1.4 percent in February.

Online gambling made a surge in March, the fourth complete month of the now-legal activity. Winnings approached $12 million last month, up 15 percent from the month prior.