Episodes involving smugglers off the California coast have increased fourfold since 2008, with more than 200 smuggling vessels spotted by American law enforcement agencies during the last fiscal year. Marijuana seizures from maritime smugglers, meanwhile, were up fourfold from just one year earlier. And some smugglers are also carrying human cargo, circumventing the security along the land border for those with the means to pay for it.

Federal officials said there was no way to know precisely how many smugglers had successfully reached California’s shores, but they believe that “a larger share” of smugglers make it through. And the flow of drugs and people into the country from the sea has clearly undercut some of the progress the authorities have made in blocking off overland supply routes.

In just a few years, officials said, drug and human trafficking off the coast here has grown into an elaborate, highly lucrative and increasingly dangerous operation, as smugglers venture farther out to sea and farther north along the coast in search of safe places to deliver their cargo undetected.

Coast Guard officials said the death of Chief Petty Officer Terrell Horne, 34, was the first time a Coast Guard member had been killed by smugglers since prohibition. But as rare as it was, the deadly encounter early last Sunday near an island off Santa Barbara also demonstrated some of the bold tactics smugglers are using here, putting law enforcement at ever greater risk.

“As the ships are going further offshore and further north, we are dealing with larger boats and more horsepower,” said Rear Adm. Karl L. Schultz, the Coast Guard commander in the region. “It does increase the challenge and the inherent danger out there to our folks on the water.”