Twelve coastal municipalities in Iwate Prefecture hit by the March 2011 earthquake and tsunami saw a record aggregate five-year drop in population, according to preliminary results of the 2015 national census.

The population of the 12 cities totaled 251,325 as of Oct. 1, down 22,761, or 8.3 percent, from the 2010 census.

Both the raw decrease and the percentage of decline were the biggest on record, the Iwate Prefectural Government said Monday.

The population decline reflects both the large numbers of people killed in the tsunami and people moving out since then amid the slow rate of recovery.

The town of Otsuchi, where more than 3,000 quake and tsunami survivors still live in temporary housing, saw a 23.2 percent drop, the largest among the 12 municipalities, followed by a 15.2 percent fall in the city of Rikuzentakata and a 15.0 percent fall in the town of Yamada.

In some municipalities, such as Miyako and Kamaishi, the rate of population decline was actually slower than before the disasters, as reconstruction workers flowed into the area, the data showed.