Environmental carrying capacity of cultured scallop in Ogatsu Bay

Representative Organization: Tohoku University

2016/04/01 - 2017/03/31
once a year

Three stations of Ogatsu Bay (St 1 - 3)

Field survey, Mooring system(Observation buoy)

We aim to survey a total amount of scallop production and the numbers of facility for scallop farming in Ogatsu Bay in order to calculate productivity of scallop and compare with a pre-quake period. In addition, we plan to measure their shell size and weight of several organs and analyze for their growth condition between two different depth conditions. The environmental capacity for scallop culture in Ogatsu Bay can be evaluated by growth condition and food availability based on a primary production (i.e., monitoring of chlorophyll a concentration). We also plan to evaluate an availability of remote sensing data for estimation of chlorophyll a concentration in waters of Ogatsu Bay comparing with regular line observation and stationary measurement by observation buoy.

By the continuous survey following the 2011 Great East Japan Earthquake, we have obtained the growth data of Japanese scallop farmed by the ear-hanging method in Ogatsu Bay for over the last five years. In comparison, it was found that there were differences in shell size, soft body weight of farmed scallops between different water layers. Specifically, the stagnation of growth in the lower layer group was first observed in 2013. Subsequently, this trend was especially seen in 2014 and 2015. The productivity (i.e., amount of scallops produced from one hanging rope) in 2013 showed at 30.9 kg per rope, while the data in 2014 and 2015 showed at 23.7 kg and 22.0 kg per rope indicating that the productivity since 2014 decreased compared to the data in 2013. The monthly mean of amount of chlorophyll a (above 20 m depth) were decreased from 2014 (197kg/month) to 2015 (126kg/month). Importantly, the decline of productivity and the stagnation of growth performance in the lower layer were shown since 2014 even though the facility numbers were increased since 2014. This could be caused by competition of food (i.e., phytoplankton) in the lower layer. We evaluated an availability of remote sensing data for estimation of chlorophyll a concentration in waters of Ogatsu Bay comparing with regular line observation. We used MODIS data mounted satellite TERRA and AQUA of NASA and GOCI data from Korea. Concentration of chlorophyll a estimated by MODIS (AQUA) data correlated to in-situ data (r = 0.70) by regular line observation in Ogatsu Bay. Additionally, we started continuous and stationary measurement by observation buoy in Ogatsu Bay association with Ogatsu branch of JF Miyagi in order to compensate to remote sensing data.

FY2016 Environmental carrying capacity of cultured scallop in Ogatsu Bay