The federal law enforcement agency that oversees all border and customs operations has arrested more people illegally crossing from Mexico into the U.S. in roughly the first six months of the 2019 fiscal year than in all of the previous year.

U.S. Customs and Border Protection said as of last week, more than 418,000 people had been apprehended since Oct. 1. In all of fiscal 2018 — from Oct. 1, 2017 to Sept. 30, 2018 — 404,142 people were taken into custody across all U.S. borders.

Exactly 99% of all apprehensions — 414,000 — took place on the southwest border in California, Arizona, New Mexico, and Texas. The other 4,000 were on the northern border or off the Atlantic and Pacific coasts.

As of last week, #BorderPatrol apprehensions for FY19TD (418,000+) surpassed total apprehensions for FY18 (404,142). Along the Southwest border, there have been 414,000+ apprehensions so far this year, compared to 396,579 total in FY18. pic.twitter.com/Qgk6xV94bQ — CBP (@CBP) April 23, 2019

Recently-ousted Homeland Security Secretary Kirstjen Nielsen told lawmakers last month she expected the department to apprehend 900,000 unauthorized immigrants at the border this year, though that figure includes people who try to enter at border crossings.

Nine Border Patrol regions or "sectors" make up the southwest border. The Rio Grande Valley Sector, the most eastern one, has seen the most apprehensions in 2019.

Since October, agents there have taken into custody more than 164,000 of the 418,000 migrants who illegally crossed from Mexico. As of last week, the sector had arrested more people in the first six-and-a-half-months of the fiscal year than the previous year, with an average of 1,100 apprehensions daily.

Some caravans, or large groups of migrants who travel together, have fled Central America for the U.S., but the majority of people arriving at the southwest border are using human smugglers and cartels to make the journey and avoid having to apply for asylum at a port of entry.

Monthly numbers tend to fluctuate with dips in the winter and hottest of summer months, and increases in the spring and fall. The number of illegal border crossers dipped to a 45-year low during President Trump's first calendar year in office in 2017.