ABC News' Pierre Thomas, Jack Cloherty and Jason Ryan report:

It might be counterintuitive, given the often-heated political rhetoric out there, but there appears to be a rather sizable decline in the number of people trying to enter the United States illegally by crossing the southwestern border.

U.S. Customs and Border Protection (CBP) statistics released today indicate that in fiscal 2011, fewer people tried to cross the southwest U.S. border illegally, but those who did were often caught smuggling drugs or money. The agency says border enforcement is much tougher because of increased manpower and its use of new high-tech tools such as surveillance drones.

The new numbers show that 340,252 people were detained at the border in last fiscal year. That number represents a 58 percent decline since 2008, and a significant drop from the 1.6 million caught in 2000.

Immigration experts say such declines likely result from a combination of the struggling U.S. economy and increased border enforcement, beginning under the Bush Administration and continuing under President Obama.

Since 2004, the CBP says, the size of the border patrol has doubled to 21,444, an increase of 886 agents from FY 2010.

But while arrests are down, the numbers reveal that a higher percentage of those arrested were drug smugglers or other kinds of criminals. CBP officers and agents seized nearly 5 million pounds of narcotics, a 20 percent increase from FY 2010 and confiscated more than $126 million in undeclared currency.

At all ports of entry, CBP officers arrested 8,195 people wanted for crimes, including murder, rape, assault and robbery.

Using high-tech enforcement tools such as aerial surveillance drones has had a significant impact on catching bad guys at the border.

According to CPB, unmanned drones now cover the southwest border all the way from California to Texas, providing critical intelligence to agents on the ground. The drone program contributed to the seizure of more than 7,600 pounds of narcotics and the apprehension of 467 individuals involved in illicit activities.

CBP's Unmanned Aircraft Systems flew more than 4,400 hours in FY 2011, 75 percent more than in 2010. But the drones are not the only airborne threat to drug smugglers.

CBP's P-3 aircraft operations resulted in the interception of 169 drug-smuggling attempts throughout the Caribbean Sea, eastern Pacific Ocean and across Central America. As a result of these interceptions, eight aircraft, 55 vessels and three self-propelled semi-submersible vehicles were seized or destroyed, yielding a seizure or disruption of more than 150,000 pounds of cocaine with a street value of more than $1.89 billion.

"In 2011, CBP made important contributions to our nation's homeland security and economic vitality," CBP Commissioner Alan D. Bersin said. "These numbers illustrate the investments made by CBP to improve border security, increase efficiencies and facilitate the flow of legal travel and trade through our nation's borders and land ports of entry."

Bersin also said that as a result of CBP pre-departure screening efforts overseas, more than 3,100 individuals who would be found inadmissible in the United States for national security, insufficient or fraudulent documents and other admissibility concerns, were denied boarding onto U.S.-bound aircraft at foreign airports.