On Thursday evening, the Italian Coast Guard received this unusual distress call: "We're without crew, we're heading toward the Italian coast and we have no one to steer."

The plea, according to the BBC, came from the Ezadeen, a 50-year-old ship initially built as a livestock carrier and sailing under the flag of Sierra Leone. Aboard the ship were 450 asylum-seekers thought to be from Syria.

It was the second such incident in a matter of days. Just before the new year, the Blue Sky M, a cargo ship carrying nearly 1,000 migrants, was intercepted by the same forces just shy of the Italian coast. One coast guard commander told reporters that the ship had its engine locked on autopilot and was hurtling toward land.

Making matters worse in that earlier incident, there was a heavy storm, which meant that rescuers had to board the ship by helicopter. "It was a race against time," the officer said. "The ship was only a few (nautical) miles away from the coast of Puglia," a region in southern Italy.

The two episodes may open a horrifying new chapter in a human-trafficking saga that has brought as many as 170,000 refugees to Italy by boat over the course of the past year or so from Africa and the Middle East. (Thousands of other migrants have died along the way.) This week, in lieu of the small, unsteady boats typical of such journeys, border forces have contended with large ghost ships full of people and abandoned by the smugglers.

“At first we wondered if it was a one-off, but it now seems to be a trend," an official from Frontex, the European Union's border control agency, told the Telegraph. "The smugglers acquire a decommissioned cargo ship, recruit a crew, pack it with migrants and then abandon them at sea, telling them to call the rescue services. It’s a very dangerous new development, especially in bad weather.”

The weather seems to be a big factor in the strategy. Larger ships can brave the rough waters of winter, extending a human-trafficking season that once predominantly ran in the spring and fall. The smugglers can then abandon the ship to evade capture by authorities.

According to Frontex, this winter has been an exceptionally busy season for those monitoring the Mediterranean borders. The agency claims that 11,400 migrants have been rescued, the vast majority of them in "distressed" circumstances, in more than 75 operations since the beginning of November.

"This level of traffic is still unprecedented for wintertime," the agency reports. "2014 could be remembered as the year that people-smuggling by sea truly became a year-round business."