By RANDAL C. ARCHIBOLD


SAN DIEGO - They move north in rickety fishing boats, often overloaded and barely seaworthy, slipping through the darkness and hidden from the watchful radar of American patrols.

Along beaches north of here, the migrants from Mexico and beyond scramble ashore and dash past stunned beachgoers, sometimes even leaving behind their boats. Drug smugglers, too, take this sea route, including one last month found paddling a surfboard north with a duffel bag full of marijuana on it.

As the land border with Mexico tightens with new fencing and technology, the authorities are seeing a sharp spike in the number of people and drugs being moved into the United States by sea off the San Diego coast.

Law enforcement authorities in the United States said the shift demonstrated the resolve of smugglers to exploit the vastness of the sea, the difficulty in monitoring it, and the desperation of migrants willing to risk crossing it.

“It’s like spillover from a dam,” said Commander Guy Pearce, who oversees the antismuggling effort for the Coast Guard in San Diego.

For generations, people have tried to swim, surf and ride boats, sometimes carrying contraband, into the United States from south of the border.

But Commander Pearce and other officials in the Department of Homeland Security say those sporadic efforts have accelerated to unprecedented levels.

The authorities arrested 136 illegal immigrants sneaking in by sea in the fiscal year that ended October 30, double the 66 marine arrests in 2007. Since October, more than 100 illegal immigrants have been arrested on the water, said Michael Carney, the Immigration and Customs Enforcement agent in San Diego who oversees a task force on marine smuggling.

The seizure of drugs, principally marijuana, has similarly skyrocketed. In the fiscal year that ended in October, the authorities seized 2,858 kilograms of marijuana in the coastal waters north of the border, a sevenfold increase from the 435 kilograms confiscated in 2007. This fiscal year, 2,767 kilograms have been found.

“This is somewhat of an alarming trend,” Mr. Carney said. “It has opened our eyes. There is still a lot we need to learn about how these organizations operate.”

The Department of Homeland Security is responding to this surge with orders for more boats and equipment.

Victor Clark Alfaro, director of the Binational Center for Human Rights in Tijuana, Mexico, who has studied smuggling, said he doubted the fence was causing the spike. Instead, Mr. Clark Alfaro said, “a new generation” of smugglers have simply had success ferrying people over the seas and are encouraging migrants to go their way. The charge is more than $4,000, roughly double what a smuggling guide would charge to lead somebody over land, he said. Marijuana smugglers, likewise, have gotten wise to the sea route.

“It’s always,” Mr. Clark Alfaro said, “a fight between technology and the ingenuity of smugglers.”

Crew members on the Coast Guard cutter Petrel said they did not believe the guard or Customs and Border Protection had enough fast boats to get to suspected smuggling boats in time.

In the end, said Petty Officer First Class Jason Tessier, a supervisor on the Petrel, “it is a matter of being in the right place at the right time.”





The Coast Guard patrols for traffickers near San Diego. Federal agents found a man paddling a surfboard carrying bags of marijuana, above.