Research on the situation of fish reproduction in southern Iwate

Representative Organization: Tohoku University

2015/04/01 - 2016/03/31
monthly

Okirai bay, Otsuchi bay, Noda bay, Sakari river

Field survey

The importance of the surf zone and the seagrass bed as a nursery ground for larval and juvenile fishes has widely recognized. We examined species composition and dynamics of larval and juvenile fishes in the surf zone and the seagrass bed to estimate the impact of the 2011 disaster and recovery process from the disaster on the environment for fish reproduction in coastal area. We also examined dynamics of juvenile Japanese flounder in Otsuchi bay and Noda bay.

We examined species composition and dynamics of larval and juvenile fishes in the surf zone and the seagrass bed in Okirai bay to estimate the impact of the Tsunami disaster and recovery process from the disaster on the environment for fish reproduction in coastal area. A total of 1445 fish larvae and juveniles, representing at least 29 species from 17 families were collected in Okirai-Urahama site in Okirai bay. In 2014, we collected 21 families, 26 species, totaling 2805 individuals. The number of species is increased, but the number of individuals is decreased. In seagrass bed in Okirai-Namiita site, we collected 24 families, 46 species, totaling 1646 individuals. The number of species and individuals are increased. The seagrass bed area is increased from 3300 to 3500 square meter. We compared stomach contents of settled juvenile Japanese flounders, stable isotope ratios of both food organisms and settled juvenile Japanese flounders before and after the Tsunami with 2009 and 2012 data in the Noda Bay. And we calculated the contribution from each food source based on stable isotope analysis. In general the ontogenic shifts of stable isotope ratios of the juvenile flounders were related with the increased dependence on fish larvae. But in 2012 the dependency on fish larvae as food source of the juvenile flounders was lower than in 2009. We found that the density of mysids determined the stomach fullness of the juvenile flounders especially for newly settled juveniles. And also the survival and/or dispersal of the juvenile flounders seemed to be affected by the density of mysids.

FY2015 Research on the situation of fish reproduction in southern Iwate