WASHINGTON (AP) — Arrests for crossing the U.S. border illegally fell slightly in March, authorities said Friday, bucking a usual spring increase amid increased immigration enforcement in Mexico.

The Border Patrol made 137,480 arrests of people entering from Mexico, down 2.3% from 140,638 arrests in February, the first time since 2017 that arrests fell in March from the previous month. Crossings typically rise as temperatures turn warmer.

Mexico detained migrants 240,000 times in the first two months of the year, more than triple from the same period of 2023, sending many deeper south into the country to discourage them from coming to the United States. While Mexico hasn’t released figures for March, U.S. officials have said Mexican enforcement is largely responsible for recent declines.

“Encounters at our southern border are lower right now, but we remain prepared for changes, continually managing operations to respond to ever-shifting transnational criminal activities and migration patterns,” said Troy Miller, acting commissioner of U.S. Customs and Border Protection.