Body condition and reproductive status of chum salmon during homing migration in Otsuchi Bay, Japan, after the 2011 Great East Japan Earthquake and Tsunami

To understand how the earthquake and tsunami on March 11 2011 affected homing chum salmon Oncorhynchus keta in Otsuchi Bay, Japan, we monitored the body condition and reproductive status at the mouth of the bay in October, November, December, and January from 2012 to 2016. The average fork length in 2014 was larger than that in 2012 and 2015, due to the high proportion of 5- and 6-year-old salmon and the low proportion of 3- and 4-year-old salmon, possibly because of the decrease in the salmon fry released by the hatchery program after the disaster. Plasma estradiol-17β (E2) concentrations in females were high in October and November and declined in December and January, whereas plasma 11-ketotestosterone concentrations in males were consistently high throughout the sampling period. Plasma 17α,20β-dihydroxy-pregnen-3-one (17α,20β-P) increased in both sexes in December and/or January. These changes were consistently observed from 2012 to 2016; however, the rise in 17α,20β-P and decline in E2 levels in female salmon in December were conspicuous in 2013 and 2014, reflecting changes in age composition. These results suggest that the earthquake and tsunami temporarily affected the age composition and the physiological condition of chum salmon returning to Otsuchi Bay.