Reporting from Nogales, Ariz. - Amid an overall drop in arrests of illegal immigrants crossing the U.S-Mexico border, an intriguing anomaly has cast a new light on human smuggling: Authorities report an almost tenfold spike in the number of Chinese people caught in the southern Arizona desert, the busiest smuggling corridor on the international line.

The Border Patrol in the Tucson sector has arrested at least 261 Chinese border-crossers this year, compared with an annual average of 32 during the last four years, officials said.

"They are the main [non-Mexicans] we catch," said field operations supervisor Juventino Pacheco of the patrol's international liaison unit in Nogales. "Lately we have been catching more Chinese than Central Americans."

When agents find Chinese migrants -- hiding in gulches, perhaps, or huddled in smugglers' vehicles -- they often request help from Dean Delap, the sector's only Mandarin-speaking agent. He taught and studied in China, but had not expected that to prove valuable in Nogales.

"Some are cooperative," Delap said. "Some are scared. They've just been arrested, they are in a new place. I put them at ease."

Chinese remain a small fraction of the overall number processed at the Nogales station -- which guards 31 miles abutting Nogales, Mexico.

The Tucson sector, where the Nogales station is located, recorded about 226,000 apprehensions this year. That is a 24% decline from the last fiscal year -- reflecting the impact of both the U.S. economic crisis and tougher border enforcement, officials said.

The great majority of those arrested were Mexicans. Chinese belong to a category known in the Border Patrol as OTMs: other than Mexicans. And they are big business for smuggling gangs that increasingly have overlapped with Mexico's violent drug mafias.