BUENAVENTURA, Colombia—The Trump administration’s bombing campaign against cocaine-smuggling speedboats is starting to have an impact on the global drug trade—but not necessarily in a good way.Thirteen months into the initiative, Colombian navy divers are detecting greater use of “parasites”—metal modules packed with cocaine that traffickers bolt onto the hulls of freighters preparing to steam out of this country’s largest Pacific port. Deep in the Amazon, smugglers have shifted shipments east, hiding drugs on boats moving through the rain forest’s vast river network. And on Colombia’s long coast, crews evade U.S. military airstrikes by hugging the shoreline in the exact same...