Post-release behaviors and movements of cultured and wild Japanese eels (Anguilla japonica) in a shallow brackish water lagoon in northeastern Japan

Migration, residency and habitat utilisation by wild and cultured Japanese eels (Anguilla japonica) in a shallow brackish lagoon and inflowing rivers using acoustic telemetry

“…Signals were detected by two receivers placed at the northeastern stations (St. 27 or 6), which were connected to the easternmost waterway (Figure 8) (see the potential detection range of the all receivers on a map in Supplementary file SFile S7). The aforementioned inference is further supported by the results of a previous study (Noda et al ., 2019) in which cultured eels were detected to have used the easternmost waterway by two receivers installed in the easternmost waterway.…”

“…To monitor spatial patterns in habitat use, the receivers were separated into four distinct quadrants based on the arrangement of the telemetry array and environmental/habitat characteristics, which were the same quadrants as set out in the previous research in 2014 (Noda et al ., 2019): “Out” (outside the lagoon; St. Out1 and St. Out2), “River” (at the four inflowing rivers; St.K1 and St.K2 for the Koizumi River, St. U1 and St. U2 for the Uda River, St. UM1 and St. UM2 for the Ume River and St. N1 and St. N2 for the Nikkeshi River), “North” (north of the dredged water route in the centre of the lagoon but not including stations at “River” and “Out”; north of St. 18 and St. 13) and “South” (south of and including St. 18 and St. 13 but not including stations at “River”) (Figure 1). The composition of the fish community has been reported to vary between the North and South quadrants (Nemoto et al ., 2007), as do the water temperature and salinity, depending on the season (Supplementary file SFile S3) (Wada et al ., 2014, 2017).…”

“…In a previous research in 2014 (Noda et al ., 2019), six wild (mean ± S.D. TL = 622.2 ± 133.1 mm, BM = 368.9 ± 247.3 g, and the age not determined) and 30 cultured (TL = 610.6 ± 24.0 mm, BM = 376.9 ± 48.7 g, and c .…”

“…To overcome the limitations of the previous study in which a small number of wild eels were released, 20 wild individuals collected on site and 12 cultured individuals were simultaneously released and their movements were monitored for >16 months using acoustic telemetry. For this study, the wild and cultured eels were released in the southern inner part of the lagoon near the river mouth where the salinity is lower (Figure 1) compared with the previous study (Noda et al ., 2019) in which cultured eels were released into the northern part of the lagoon with higher salinity condition. It was examined whether large cultured eels (BM > 200 g) indicate short resident time in the lagoon regardless of the released site in the brackish water area with different salinities.…”

“…(b) Locations of the acoustic receivers (closed circles). The star indicates the release point in this study and the triangle indicates the release point in the previous research in 2014 (Noda et al ., 2019). The dotted lines within Matsukawa‐ura lagoon represent the waterways that have been dredged for navigation.…”