Immigration from Mexico to the United States, especially illegal immigration, began to drop off in 2006 and continued its downward slide into this year, said a report by the Pew Hispanic Center, which looked at population surveys from both countries and US law enforcement data.

Between March 2008 to March 2009, the "estimated annual inflow of immigrants from Mexico was lower than at any point during the decade," bottoming out at about 175,000 immigrants, the report said, citing data from the US Census Bureau's Current Population Survey.

In the previous two years, the number of immigrants crossing from Mexico to the United States was around twice that figure, the report said.

Statistics from Mexico's National Survey of Employment and Occupation (ENOE) also showed a marked decline in the number of Mexicans heading to the United States.

The statistics from ENOE showed that the immigrant flow from Mexico to the United States has fallen by around 20 percent a year since 2006, from more than a million people in the 12 months starting February 2006 to 814,000 for the same period in 2007-2008 and to 636,000 in 2008-2009.

The figures from Mexico were markedly higher than the US census figures because the Mexican figures cover a broad spread of migrants -- anyone who has left the country -- while the US figures track only people whose principal residence is in the United States.

Information from the US Border Patrol appeared to confirm the decline in the number of Mexicans coming to the United States.

In 2008, the number of Mexicans who were apprehended by the US Border Patrol as they tried to enter the United States illegally -- 662,000 -- was 40 percent down from the 1.1 million who were caught at the border in 2004.

Indeed, 2008 saw the lowest number of apprehensions of would-be illegal immigrants from Mexico by the US border guard in 25 years.

As for the possible reasons for the drop-off in Mexican immigration to the United States, researchers said it could be due to the weak US economy and tougher border enforcement measures.

A third of all foreign-born US residents and two-thirds of Hispanic immigrants to the United States come from Mexico, the report said.

Nearly everyone who leaves Mexico heads for the United States, which is currently home to one in 10 people who were born in Mexico.

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