Administration officials credit a policy of returning asylum-seeking migrants to Mexico and an end to a policy referred to by critics as "catch and release."
The illegal stocks, muzzles and other items were intercepted in recent months. "There was no attempt to hide the importation attempt," CPB spokesperson Jaime Ruiz told NPR.
"Although the new federal regulation allows us to apply that all 2,000 miles along the Southwest border, we're not going to do that," Mark Morgan told NPR.
John Sanders is expected to make his resignation effective July 5, two officials say. The move comes after hundreds of children were removed from a facility without adequate food and sanitation.
Reports of children detained in crowded and unsanitary conditions long beyond the maximum legal limit have created a new controversy over the administration's immigration policies.
The photographs of license plates and people inside vehicles were taken over a six-week period at a single U.S. land-border point, the Customs and Border Protection agency says.
Florida officials say they were informed of the migrant release plan by the federal government. They are scrambling to prepare for an influx of asylum-seekers.
The child's mother informed federal agents that her 2 ½-year-old son was sick after they were taken into custody last month on the north bank of the Rio Grande in El Paso, Texas, U.S. officials say.