Arrests of Venezuelans at the border have plummeted. That’s because they’re stuck.

Venezuelan migrants often have a quick answer when asked to name the most difficult stretch of their eight-country journey to the U.S. border, and it’s not the dayslong jungle trek through Colombia and Panama with its venomous vipers, giant spiders, and scorpions. It’s Mexico.

“In the jungle, you have to prepare for animals. In Mexico, you have to prepare for humans,” Daniel Ventura said after three days walking through the Darien Gap and four months waiting in Mexico to enter the U.S. legally using the government’s online appointment system, called CBP One. He and his family of six were headed to Fort Atkinson, Wisconsin, where he has a relative.

Mexico’s crackdown on immigration in recent months – at the urging of the Biden administration – has hit Venezuelans especially hard. The development highlights how much the U.S. depends on Mexico to control migration, which has reached unprecedented levels and is a top issue for voters as President Joe Biden seeks reelection.

Arrests of migrants for illegally crossing the U.S.-Mexico border have dropped so this year after a record high in December. The biggest decline was among Venezuelans, whose arrests plummeted to 3,184 in February and 4,422 in January from 49,717 in December.

While two months do not make a trend and illegal crossings remain high by historical standards, Mexico’s strategy to keep migrants closer to its border with Guatemala than the U.S. is at least temporary relief for the Biden administration.

Large numbers of Venezuelans began reaching the U.S. in 2021, first by flying to Mexico and then on foot and by bus after Mexico imposed visa restrictions. In September, Venezuelans briefly replaced Mexicans as the largest nationality crossing the border.

Mexico’s efforts have included forcing migrants from trains, flying and busing them to the southern part of the country, and flying some home to Venezuela.

Last week, Mexico said it would give about $110 a month for six months to each Venezuelan it deports, hoping they won’t come back. Mexican President Andres Manuel López Obrador extended the offer March 26 to Ecuadorians and Colombians.

“If you support people in their places of origin, the migratory flow reduces considerably, but that requires resources and that is what the United States government has not wanted to do,” said Mr. López Obrador, who is barred by term limits from running in June elections.

Migrants say they must pay corrupt officials at Mexico’s frequent government checkpoints to avoid being sent back to southern cities. Each setback is costly and frustrating.

“In the end, it is a business because wherever you get to, they want to take the last of what you have,” said Yessica Gutierrez, who left Venezuela in January in a group of 15 family members that includes young children. They avoided some checkpoints by hiking through brush.

The group is now waiting in Mexico City to get an appointment so they can legally cross the U.S.-Mexico border. To use the CBP One app, applicants must be in central or northern Mexico. So Ms. Gutierrez’s group sleeps in two donated tents across the street from a migrant shelter and check the app daily.

More than 500,000 migrants have used the app to enter the U.S. at land crossings with Mexico since its introduction in January 2023. They can stay in the U.S. for two years under a presidential authority called parole, which entitles them to work.

“I would rather cross the jungle 10 times than pass through Mexico once,” said Jose Alberto Uzcategui, who left a construction job in the Venezuelan city of Trujillo with his wife and sons in a family group of 11. They are biding time in Mexico City until they have enough money for a phone so they can use CBP One.

Venezuelans account for the vast majority of 73,166 migrants who crossed the Darien Gap in January and February, which is on pace to pass last year’s record of more than 500,000, according to the Panamanian government, suggesting Venezuelans are still fleeing a country that has lost more than 7 million people amid political turmoil and economic decline. Mexican authorities stopped Venezuelan migrants more than 56,000 times in February, about twice as much as the previous two months, according to government figures.

“The underlying question here is: Where are the Venezuelans? They’re in Mexico, but where are they?” said Stephanie Brewer, who covers Mexico for the Washington Office on Latin America, a group that monitors human rights abuses.

Mexico deported only about 429 Venezuelans during the first two months of 2024, meaning nearly all are waiting in Mexico.

Many fear that venturing north of Mexico City will get them fleeced or returned to southern Mexico. The U.S. admits 1,450 people a day through CBP One with appointments that are granted two weeks out.

Even if they evade Mexican authorities, migrants feel threatened by gangs who kidnap, extort, and commit other violent crimes.

“You have to go town by town because the cartels need to put food on their plates,” said Maria Victoria Colmenares, who waited seven months in Mexico City for a CBP One appointment, supporting her family by working as a waitress while her husband worked at a car wash.

“It’s worth the wait because it brings a reward,” said Ms. Colmenares, who took a taxi from the Tijuana airport to the border crossing with San Diego, hours before her appointment.

Texas Republican Gov. Greg Abbott has touted his own efforts to explain the recent reduction in illegal crossings in his state, where at least 95% of Border Patrol arrests of Venezuelans occur. Those have included installing razor wire, putting a floating barrier in the Rio Grande, and making plans to build a new base for members of the National Guard.

U.S. Homeland Security Secretary Alejandro Mayorkas has mostly credited Mexico for the drop in border arrests.

Some Venezuelans still come north despite the perils.

Marbelis Torrealba arrived in Matamoros, across the border from Brownsville, Texas, with her sister and niece this week, carrying ashes of her daughter who drowned in a boat that capsized in Nicaragua. She said they were robbed by Mexican officials and gangs and returned several times to southern Mexico.

A shelter arranged for them to enter the U.S. legally on emergency humanitarian grounds, but she was prepared to cross illegally.

“I already experienced the worst: Seeing your child die in front of you and not being able to do anything.”

This story was reported by The Associated Press. Mr. Spagat reported from Tijuana, Mexico, and Ms. Gonzalez reported from Matamoros. Associated Press reporter Rebecca Santana in Washington, D.C., also contributed.