FILE - In this Wednesday, Nov. 21, 2018 file photo, United States Border Patrol agents stand by a vehicle near one of the…
FILE - In this Nov. 21, 2018 file photo, United States Border Patrol agents stand by a vehicle near one of the border walls separating Tijuana, Mexico and San Diego, in San Diego.

The number of migrants apprehended along the U.S.-Mexico border has declined sharply since May 2019, according to data released Thursday by U.S. Customs and Border Protection (CBP).

A CBP official told reporters Thursday that the number of people apprehended or viewed as "inadmissible" totaled 40,620 last month, a 72% decrease from the more than 144,000 recorded at the peak of the border crisis last May.

During Thursday's press call, border officials attributed the seven-month decline to the Trump administration's policy initiatives aimed at deterring illegal border crossings.

Despite the drop, the December apprehensions number is not especially low, according to Migration Policy Institute analyst Jessica Bolter.

FILE - Members of the Border Patrol and U.S. military talk with migrants who illegally crossed the border between Mexico and the U.S. to request political asylum, as seen from Ciudad Juarez, Mexico, July 6, 2019.

"Looking back at apprehensions in the month of December, this number is the fourth highest between 2012 and 2019. So, it's solidly in the middle," she said.

Even so, Bolter noted that apprehensions have been declining month after month since May.

"This indicates that there's something going on other than seasonal factors that's affecting migration flows," she said. "The combination of MPP [Migrant Protection Protocols] and Mexico's increased enforcement, which both mainly target Central Americans, is clearly having a deterrent effect."

Under MPP, also known as "Remain in Mexico," migrants are forced to await U.S. immigration court dates in Mexico. Human rights advocates say the program deters people with legitimate asylum claims from seeking protections in the United States.

In December, family units accounted for 12,064 people who crossed the border without authorization and were stopped by U.S. Border Patrol agents. There were 3,707 unaccompanied children and 24,788 single adults, down 4% from November.

Overall, CBP reports a 69% decline in unaccompanied children and a decrease across all key demographics since May.