By dawn, the frenzied scramble had come to an end and 1,280 kilograms of cocaine — worth about $37 million on the street — were in federal hands

SAN JUAN, P.R. — With its navigation lights off, the 35-foot speedboat raced north toward Puerto Rico one night this month, its two large engines at full throttle. Above, a Coast Guard helicopter chased it and then let loose a few warning shots. But the boat roared ahead. Then, thwack, the crew on the copter shot out one of engines.

By dawn, the frenzied scramble had come to an end and 1,280 kilograms of cocaine — worth about $37 million on the street — were in federal hands, much of it scooped from the Caribbean Sea, where the smugglers had tossed the bales. An interagency task force of federal law enforcement, the Coast Guard and the Puerto Rico Police Department confiscated the drugs and arrested two men from the Dominican Republic. A third man had jumped overboard and was never found.

It was one in a string of increasingly common high-profile drug hauls and arrests playing out in and around Puerto Rico and nearby Caribbean islands, a trail mythologized in the cocaine cowboy era of the 1980s, when a seemingly endless supply of drugs flowed from this region into Miami. Seizures of cocaine, the most profitable drug for smugglers, have nearly quadrupled here since 2011. Over the past three years, the seizures of cocaine headed for the United States from South America have risen by as much as 20 percent, according to federal drug enforcement officials.

The sharp increase in the drug trade here is a sign of shifting patterns by traffickers in Colombia and Venezuela who are looking for new ways to import cocaine into the United States. The shift comes amid continuing violence among drug gangs along the United States-Mexico border, where most drugs continue to enter the United States, and a law enforcement crackdown that has made smuggling there an increasingly risky proposition. Seizures and arrests in and around the island continue to mount.

In April, a boat made landfall in Puerto Rico. Three passengers fled, but agents found 1,530 kilograms of cocaine on the boat. Days earlier, another boatload, this one with 1,774 kilograms of cocaine, was intercepted.