– The Trump administration's focus on the southern border has closed some gaps in immigration enforcement but expanded a problem, law enforcement officials said Wednesday: immigrants sneaking into California by sea.

Migrants enter in various ways, including on personal watercraft and small, open-top motorboats known as pangas that often arrive under cover of darkness, said Jeremy Thompson, Customs and Border Protection's director of marine operations in San Diego.

On Sunday, the 87-foot Coast Guard patrol boat USCGC Petrel stopped a vessel with 12 migrants from Mexico aboard near California's southern maritime border. On Tuesday, a Customs and Border Protection team stopped another group, disabling a boat with gunfire after it failed to stop, and detaining eight more migrants, he said.

Chief Patrol Agent Rodney Scott said that he expects smugglers to adjust their tactics as U.S. officials alter theirs, and he believes that the United States is taking away most of the "low-risk ways" to get into the country.

"We've been busy out here," Scott said. "Once the rhetoric started with the wall, it definitely picked up in the maritime."

Across Southern California, 1,022 migrants were intercepted at sea in the fiscal year ending Sept. 30, Coast Guard officials said. That was up from 213 in 2017 and 142 in 2016. Those numbers are small compared with the 521,090 apprehensions CBP reported at the southern border in 2018. But the practice at sea is lucrative for those who facilitate it.