Kyodo via Reuters Boats containing dead bodies from North Korea have continued to show up along Japan's west coast. North Korea usually tightly controls its borders to prevent defections. This suggests that Kim Jong Un is losing his grip over his country's border security and his citizens' economic ventures, experts told BI. The seemingly endless appearances of "ghost ships" full of dead North Koreans on the shores of Japan is indicative of Kim Jong Un's weakening grip over his citizens, experts say. The latest took place last week, when a capsized boat containing the decayed remains of seven bodies washed ashore in Kanazawa, a city on Japan's west coast. A badge portraying former North Korean leaders Kim Il Sung and Kim Jong Il was also found nearby. It was the second such discovery in Japan this month. The number of ghost ships — vessels discovered with no living crew — reached 104 last year, the highest since authorities started collecting data in 2013, Japan's Kyodo news agency quoted the national coast guard as saying. It remains unclear exactly who these people were, or why they showed up in Japan — experts have posited theories including food insecurity in North Korea, annual quotas imposed on fishermen, and a deal for fishing rights between North Korea and China. A new theory suggested to Business Insider this week is that the increasing arrivals of these boats indicate Kim Jong Un's weakening grip over his country and its people. It came from Professor Hazel Smith, a researcher at the School of African and Oriental Studies in London. Google Maps/Business Insider North Korea, notoriously, tightly controls its borders to prevent defections.