The U.S. Border Patrol arrested nearly 10,000 unaccompanied immigrant children and families caught illegally crossing the border with Mexico in August, a 52% jump from August 2014, according to statistics published by the agency Monday afternoon, reports the Associated Press.

Since the start of the fiscal year in October, border agents have arrested more than 35,000 children traveling alone and more than 34,500 people traveling as families, mostly mothers and children. The total number of arrests for the year is down nearly 50% compared with a year ago, but border agents have reported a jump in arrests since July.

The Border Patrol reported arresting 6,424 unaccompanied immigrant children and families in August 2014, compared to 9,790 this year.

It's unclear exactly what has led to the overall decrease in border arrests of families and children, but Mexico has stepped up enforcement along its southern border.