Immediate impact of the tsunami associated with the 2011 Great East Japan Earthquake on the Plecoglossus altivelis altivelis population from the Sanriku coast of northern Japan

Abstract

The huge tsunami associated with the 2011 Great East Japan Earthquake severely impacted the ecosystems on the Sanriku coast of Japan. The life history traits of ayu, Plecoglossus altivelis altivelis, which have a one-year amphidromous life history, were investigated by otolith analyses in two rivers of the Sanriku coast just after the tsunami compared with results before the tsunami to reveal the immediate impact of the tsunami. Hatching date compositions differed between the upstream migrants before and after the tsunami. The migrants after the tsunami were solely composed of fish hatched during October and November, whereas the migrants before the tsunami were mostly composed of fish hatched in September. Discrepancies between the hatching dates of the migrants and drifting larvae (hatched larvae) indicate that selective mortality of early-hatched fish occurred during the tsunami. Differences in otolith Sr:Ca ratios between upstream migrants before and after the tsunami suggest that fish surviving the tsunami inhabited saline water and earlyhatched fish that inhabited the estuary decreased selectively in number because of the severe erosion around the river mouth. The oceanic growth period shortened in accordance with the change in hatching date. These results show that the tsunami drastically altered the ecology of P. altivelis altivelis on the Sanriku coast.

High growth performance in the early ontogeny of an amphidromous fish, Ayu Plecoglossus altivelis altivelis, promoted survival during a disastrous river spate

“…Error bars indicate standard deviations. The horizontal line shows the boundary between brackish and fresh water for the otolith Sr/Ca ratio (2.4 × 10 –3 weight %) of the ayu (Hata et al, 2016). The vertical grey zone indicates the period of heavy rain (the 2018 flood) in the Takahashi River watershed, Okayama, Japan, between 28 June 8 and July 2018…”

“…Following a reported value of otolith Sr/Ca ratio in fresh water (Hata et al, 2016), the boundary between brackish and fresh water was determined as an otolith Sr/Ca ratio of 2.4 × 10 –3 (weight %) using a five‐day moving mean to reduce measurement errors by EPMA. The date at upstream migration of each individual was defined as the date when the Sr/Ca ratio first scored <2.4 × 10 –3 (weight %).…”

Facultative amphidromy involving estuaries in an annual amphidromous fish from a subtropical marginal range

“…To examine the migration history, we defined the range of otolith Sr:Ca in seawater, brackish water and freshwater. Normally, the otolith Sr:Ca (× 10 3 ) of P. a. altivelis reared in freshwater is <2.4 (Hata et al ., ). However, this indicator was not consistent with our specimens.…”

“…Although all individuals were collected from freshwater, the Sr:Ca at the posterior edge of the otolith ( i.e ., the time when the individuals were captured) was between 3.0 and 4.0, or was sometimes >4.0 (Figure ). As the otolith Sr:Ca is affected by the environmental water Sr:Ca (Brown & Severin, ), and water Sr:Ca sometimes shows a high ratio in freshwater in response to the soil content (Müller, ; Singh et al ., ) and increases in the process of groundwater soil‐salt precipitation (Palmer & Edmond, ), we assumed that the water Sr:Ca in the Yakugachi River was higher than that of other examined rivers (Hata et al ., ; Kuroki et al ., ; Ma et al ., ; Otake & Uchida, ). In the present study, we calculated the mean value of the daily changes in otolith Sr:Ca of 48 individuals to decrease any outlier effect.…”

Impact of the huge 2011 Tohoku-oki tsunami on the phenotypes and genotypes of Japanese coastal threespine stickleback populations

“…In the 21st century, several huge tsunamis have occurred: the 2004 Indian Ocean tsunami, the 2010 Chilean tsunami, and the 2011 Tohoku-oki tsunami. Previous studies have focused on the effects of tsunamis on aquatic ecosystems 8 – 19 . In these cases, the tsunamis disturbed the habitats of wild aquatic animals by changing landforms, deteriorating water and soil qualities, and bringing in sediments and debris.…”