Acoustic monitoring data of anuran species inside and outside the evacuation zone of the Fukushima Daiichi power plant accident

Study Extent

The study area and sampling sites are the same as those examined by Yoshioka et al. (2015) and Fukasawa et al. (2017). The area is located in the eastern part of Fukushima Prefecture, northeastern Japan and is enclosed within the following four sets of coordinates: (37.80137°N, 140.53747°E), (37.80136°N, 141.00048°E), (36.99588°N, 141.00048°E), and (36.99588°N, 140.53747°E). The study area contains the evacuation zone, which has been divided into three subzones since October 2013: a zone designated in preparation for lifting the evacuation order (≤20 mSv/year; Zone 1), a restricted residence area (20–50 mSv/year; Zone 2), and a difficult-to-return-to zone (>50 mSv/year; after five years, the air dose rate will be >20 mSv/year; Zone 3). Note that the areas of these subzones have been reviewed annually, and the evacuation order has been partly canceled. In 2014, we set up 52 monitoring sites inside and outside the evacuation zone (33 sites outside the evacuation zone, six sites in Zone 1, seven sites in Zone 2, and six sites in Zone 3). In 2015, we added new five monitoring sites to the sites in 2014 and set up 57 monitoring sites in total (33 sites outside the evacuation zone, eight sites in Zone 1, ten sites in Zone 2, and six sites in Zone 3). All monitoring sites were located within schoolyards (including those that had been converted into community centers) to minimize differences in the local site conditions and to examine the frog assemblages in the urban and rural landscapes that were heavily altered by the sudden halt in usual land management owing to the evacuation.

Sampling

A digital voice recorder (DS-850, Olympus, Tokyo, Japan) was installed at each monitoring site during the period from May to July each year to record the songs of birds and the calls of frogs (see Fukasawa et al. [2017] for further details). In 2014, the recorders were set up at the sites until 21st May and collected after 8th July. In 2015, they were set up until 14th May and collected after 5th July. To record the calls of frogs at night according to the methods of Fukuyama et al. (2009), the recorders were used in a timed-recording mode from 20:00 to 20:10 (total 10 min) daily until the batteries were depleted. The recorders were fixed to tripod stands at a height of about 0.9 m. The recorded data were split into 20-sec segments in MP3 (124 kbps) format, which was treated as the minimum sample unit. We manually identified frog species from the acoustic data. Because the number of segments was very large, we chose a subset of segments evenly spaced throughout the recording period: four segments per day for four days (May 25th, and June 5th, 15th, and 25th) per site per year, in principle. A total of 1,059 of the 76,020 recorded segments and 903 of the 73,260 recorded segments were chosen in 2014 and 2015, respectively (due to battery depletion of recorders, considerable amount of data could not be obtained on 25th June in 2015). Note that other checked segments were also added to the sample set; for example, segments from June 20th were sometimes checked when no acoustic files were obtained on June 25th as a result of dead batteries at some sites. Frog species that appeared in each segment were identified and recorded as follows. First, authors experienced with ecological field work screened the segments in which frogs other than Japanese tree frogs (Hyla japonica) or bullfrogs (Lithobates catesbeiana) were calling. The calls of these species can be easily identified by field ecologists without expertise in frogs because their calls are simple, common, and conspicuous in eastern Japan. Then, the segments with calls of other frog species (including sounds judged to be possible frog calls) were checked and identified by frog experts, namely Dr. N. Matsushima, who is one of the authors and who has conducted research on frogs in the evacuation zones in 2012 (Matsushima et al., 2015), or employees of Regional Environmental Planning Inc. (Note that a part of segments was firstly checked by these experts without screening). For the segments that included calls that were difficult to identify at the species level, the authors, including Dr. Matsushima, made the final determination.

Quality Control

All species were identified by the authors or by professional experts as mentioned above. The scientific nomenclature used was in accordance with the Herpetological Society of Japan (2019).

Method steps

1. Presence-absence records with uncertain identification of species were removed.
2. Presence-absence records were summed up as daily data.

1. Amphibia
   rank: class

Fukushima, Japan