When the policy took effect in the Yuma sector of the Border Patrol in May, the arrests reached 14,000. In October, they fell 94%, or about 800, and have stayed there since, making Yuma the second slowest of the agency's nine sectors on the U.S.-Mexico border, according to statistics quoted by the Associated Press.
There were several reasons for the recent fall. Anthony Porvaznik, head of the Yuma sector of the Border Patrol, said the so-called Migration Protection Protocols were a major deterrent, based on the agents' interviews with those arrested.
"Their whole purpose was to be launched in the United States and, once taken off the shelf for them, and they could no longer be released in the United States, it really decreased the amount of traffic that passed through here," Porvaznik said.
In the neighboring sector of Tucson, arrests increased every month from August to December, contrary to a trend across the border and making it the second busiest corridor after the Rio Grande Valley in Texas. Porvaznik attributed the Tucson increase to the policy's late implementation.
More than 55,000 asylum seekers have been returned to Mexico to await hearings until November, 10 months after the policy's first effect in San Diego.
Critics said the policy was unfair and exposed asylum seekers to extreme violence in Mexico's border cities, where lawyers are hard to find.
The American Civil Liberties Union and other groups have asked to suspend the policy during a legal challenge. O US 9th Circuit Court of Appeals heard arguments on October 1 and did not indicate when to decide.
Last Tuesday, critics won a separate lawsuit when a federal judge in San Diego said asylum seekers who returned to Mexico from California deserved access to lawyers hired before and during major interviews to determine whether they could stay in the U.S. while the processes continued.
In Yuma, asylum seekers are kept in short-term cells until the space is opened to return to Mexicali through a neighboring sector in California.
While illegal crossings fell in Yuma, asylum seekers still signed up for a waiting list to enter the United States on an official ticket in San Luis, Arizona.
US Customs and Border Protection called the Mexican shelter that manages the list to say how many asylum claims he would process each day. The shelter estimated the wait at three to four months.
The Associated Press contributed to this report.