Updated

Border Patrol arrests dipped 17 percent this year, a drop in undocumented immigration the government attributes to heightened enforcement.

Some 463,000 people were arrested by the Border Patrol during the federal government’s fiscal year, which ended Sept. 30, said Homeland Security Secretary Janet Napolitano. That’s down 556,032 from the previous 12 months, the fifth straight year of declines.

Many of the arrests occurred at the nearly 2,000-mile border with México. The agency said about 97 percent of undocumented immigrants were arrested along the southern border, with nearly all the rest being detained attempting to come in from Canada.

“The manpower, the technology, the infrastructure all has enabled us to be able to really slow that flow of illegal immigrant traffic," Napolitano said at a news conference at the San Ysidro border crossing with Tijuana, Mexico.

She added that the weak economy and enforcement against employers helped explain why fewer people are getting caught crossing the border. She also credited President Barack Obama for dispatching an all-time high of 20,500 agents and 1,200 National Guard troops for enforcement

The increase in border patrol in a continuation of policy over the last 15 years, said Peter Nuñez, a former U.S. attorney in San Diego and an advocate of stronger enforcement.

President Bill Clinton launched a crackdown in San Diego and El Paso, and President George W. Bush doubled the size of the Border Patrol to 20,000 agents and, at one point, had 6,000 National Guard troops along the border.

That may explain why Border Patrol arrests have plummeted since 2000, when nearly 1.7 million were detained.

“It's been a long process over several administrations,” said Nunez, who teaches immigration policy at University of San Diego. “They are reaping the rewards.”

But Enrique Morones, an activist who supports looser immigration policies, though enforcement has discouraged border crossing, the main reason is the economy.

“If there are fewer jobs available, fewer people come,” said Morones, president of Border Angels, which provides water to migrants crossing the border.

The Associated Press contributed to this article.