(CNN) -- Mexican authorities said Monday that they've spotted a troubling immigration trend: large numbers of migrants abandoned at sea by traffickers.
Every month, Mexico's navy says it rescues about 150 stranded migrants, left adrift in overloaded boats off the country's Pacific coast.
As part of the scam, officials said in a statement, traffickers tell the migrants that there has been an equipment failure and promise to return but never do.
The immigration and maritime authorities said the frequency of that approach -- about 10 or 12 times per month -- inspired them to issue a warning on Monday: "Do not allow yourself to be fooled and put your life at risk by leaving it in the hands of people without scruples whose only goal is obtaining money without caring about the lives of other human beings."
Authorities have long warned of the dangers of illegal border crossings, often focusing on perilous desert treks by land.
And in the past five years, maritime border crossings into the United States have become a "new frontier," said David Shirk, a professor of political science at San Diego State University and an expert on Mexico and border security.
"It's a reflection of the fact that is has become significantly more difficult to cross the border by land," he said.
That means the Border Patrol and the U.S. Coast Guard will likely need more resources, he said, "to address not only the illegal activity, but also the different kinds of risks that implies for people who are putting themselves in that situation."
"We're likely to see a dramatic increase now in drownings and other kinds of water fatalities and other kinds of danger associated with crossing in the water," he said.
The statement from Mexican authorities on Monday suggests that attempted border crossings by boat are drawing increasing concern. But it isn't a new phenomenon.
In 2009, U.S. officials said Mexicans smuggling drugs and migrants into the United States were increasingly turning to the Pacific Ocean for a short sail to the California coast.
"We've seen a huge spike in smuggling by water," Lauren Mack, a spokeswoman for the Immigration and Customs Enforcement office in San Diego, said in 2009.
Despite the dangers of border crossings, new figures released by the Pew Research Center on Monday indicate that more than a third of Mexicans surveyed say they would move to the United States if they could.
In a national opinion survey of 1,000 Mexicans conducted last month, more than 60% said they would not move to the United States even if they had the means and opportunity to do so, but a "a sizable minority" of 35% said they would move to the United States if they could. And 20% said they would emigrate without authorization, according to Pew.
Immigration is expected to be one of the topics on the table when U.S. President Barack Obama travels to Mexico this week.
CNNMexico.com and CNN's Arthur Brice, Rene Hernandez and Rafael Romo contributed to this report.