The number of migrant families taken into custody along the U.S. border with Mexico remained nearly unchanged from June to July, said government data released Wednesday, an indication that the Trump administration’s separation of thousands of parents and children did little to deter others from attempting the journey.

U.S. border agents arrested 9,258 “family units,” along the southwest U.S. border last month, down slightly from 9,434 in June and 9,485 in May.

The administration cited a springtime surge of parents crossing illegally with children as justification for its “zero tolerance” initiative, which led to the separation of about 2,500 families between May 5 and June 20, when public outcry forced President Donald Trump to end the practice.

Since then, some of the policy’s defenders have argued that the separations would have had a stronger deterrent effect if allowed more time. They said its true impact would not be apparent until word of the crackdown had spread to rural Central America, prompting parents to reconsider travel plans.

But the July arrest totals suggest the separations made little difference. A Department of Homeland Security senior official said the agency hasn’t concluded why there were fewer apprehensions of unaccompanied minors. But the official noted that, in July, family groups accounted for a larger share of unauthorized border-crossers — 29.6 percent.

In total, U.S. agents took 39,953 migrants into custody along the border in July, down from 42,838 in June. Those figures were significantly lower than the 50,000 or more arrests made each month in March, April and May, an increase that left Trump demanding tougher measures.

Illegal migration along the Mexico border typically increases in spring before falling again during the summer when temperatures peak, raising the risk of heat stroke and death from exposure.