The number of illegal immigrants apprehended at the U.S.-Mexico border dropped in January for the first time after ticking up since April last year.

Customs and Border Protection said 35,822 migrants were captured by border officials in January. That number is down from more than 40,000 in December, a month that saw the most apprehensions in President Trump's first year in office.

The number of apprehensions and inadmissibles, which includes family units and unaccompanied minors, has ticked up since last spring despite its hitting a 45-year low in 2017.

The number of children and people claiming to be family units has ticked up from 8,000 in October to 12,200 in December. It dropped to under 9,000 in January.

DHS uses border apprehensions as a rough proxy for how many people are trying to enter the country, so a drop is generally seen as a sign that fewer attempts are being made.

Department of Homeland Security acting press secretary Tyler Houlton said the problem is still a serious concern for CBP because it represents a loophole in the system that people are able to game in order to gain admission to the U.S.

"Once again, this month we saw an unacceptable number of [unaccompanied minors] and family units flood our border because of these catch and release loopholes," Houlton said in a statement.

"DHS front-line personnel are required to release tens of thousands of unaccompanied alien children and illegal family units into the United States each year due to current loopholes in our immigration laws," he added. "To secure our borders and make America safer, Congress must act to close these legal loopholes that have created incentives for illegal immigrants and are being exploited by dangerous transnational criminal organizations like MS-13."