The number of people who illegally crossed the southern border or arrived at a port of entry to claim asylum has declined for a sixth consecutive month since peaking at the height of the humanitarian crisis in May.

Acting U.S. Customs and Border Protection Commissioner Mark Morgan announced Monday that 42,649 people were apprehended or showed up to claim asylum along the U.S.-Mexico border in November. That number is down from more than 144,116 in May.

The number of arrests has dropped significantly since Mexico deployed more federal police and military to the United States and Guatemalan borders to deter illegal immigration after President Trump followed through on a threat to impose tariffs on Mexican imports if the country did not take action.

The Trump administration also began turning away asylum seekers arriving at border crossings, limiting the number of people who can present their cases per day. It then implemented the Migrant Protection Protocols, which mandate the large majority of asylum seekers be returned to Mexico while their case waits to be heard by a U.S. federal immigration judge.

The number had dropped to 104,311 in June, 81,777 in July, 62,707 in August, 52,546 in September, and 45,250 in October. It is now on par with the usual number of monthly encounters of people on the southern border.

Morgan, speaking at a press conference at CBP headquarters in Washington on Monday morning, called the overall decline "staggering in a very positive way."

U.S. Customs and Border Protection

CBP breaks down border arrivals into two categories: arrests of illegal crossers and those claiming asylum at official crossing points. CBP uses the number of arrests as an indicator of how many people tried to illegally enter the country since it is not able to stop every person who tries.

Border Patrol agents who work between crossing posts arrested 33,510 people in November. CBP Office of Field Operations officers at crossing roads saw 9,139 people surrender and claim a credible fear of being returned home, the start of the asylum process.

The biggest share of the 144,116 people CBP encountered at the border in the month of May were families, including 88,000 people who arrived with a family member. That number is down 85% to 13,000 in November.

The majority of people arrested after being caught illegally crossing into the U.S. last month were adults, not unaccompanied children or people traveling with a family member.

Arrests of people entering without documentation slowly moved up from about 300,000 in 1970 to between an average of 1 million and 1.5 million each year from the mid-1980s through 2006, according to Border Patrol data. October’s total of 35,000 is a rate consistent with 420,000 arrests per year.