In the past two weeks, at least seven boats have arrived in Akita, all of them bearing signs that they came from North Korea. One of them carried eight live crew members to Yurihonjo, a medium-size port town in Akita, where they were kept in police custody for more than a week before being transferred to an immigration facility in Nagasaki last Saturday. Japan’s Immigration Bureau said the men would be returned to North Korea.

With tensions mounting on the Korean Peninsula as the North’s nuclear and missile programs continue to advance, the arrival of this ghostly armada has stoked anxiety in Japan, where residents are questioning the motives of the fishermen and those who may have sent them.

“I am wondering why so many of these have all of a sudden come in such a short time,” said Kazuko Komatsu, 66, who lives in a house close to the marina in Yurihonjo. North Korea, she said, “is a mysterious country. We don’t know so much. I don’t know if they are coming here to escape or whether they just accidentally drifted here.”