"The U.S. economic slump, more economic stability in some Mexican areas, increased U.S. enforcement on the border and in the interior plus the drop in the total fertility rate in Mexico are likely among the reasons for this drop," said University of Texas sociology professor Nestor P. Rodriguez.
"On the other hand, arrests by federal authorities for immigration offenses is rising, no doubt partly due to greater enforcement efforts," said Rodriguez, who has spent decades studying Latino migration and the impact of U.S. immigration policies on immigrant communities.
Suspects arrested by the Marshals Service for federal criminal immigration offenses increased from 8,777 in 1994 to 82,438 in 2010.
In a seven-year span ending in 2010, the number of border patrol officers nearly doubled, from 10,819 to 20,558, the study says.
The number of Mexican citizens serving a federal prison term for an immigration offense increased from 2,074 in 1994 to 17,720 in 2010. Nine out of 10 immigration offenders in federal prison were convicted of illegal re-entry or illegal entry offenses. Ten percent were convicted of alien smuggling.
More than eight out of 10 deportable aliens in 2010 were citizens of Mexico. An increasing share of deportable aliens are coming from countries in Central America, 12 percent in 2010, up from 3 percent in 2002.