Environmental carrying capacity of cultured scallop in Ogatsu Bay

Representative Organization: Tohoku University

2016/01/01 - 2016/01/31
once a year

Two stations of Ogatsu Bay (St 1 & 2)
0150_R01.pdf

Field survey

Total amount of scallop production and the numbers of facility for scallop farming in Ogatsu Bay were obtained and used for calculation in order to compare with a pre-quake period. In addition, shell size and weight of several organs of the cultured scallops by ear hang method were measured and analyzed for their growth condition between two different depth conditions. The environmental capacity for scallop culture in Ogatsu Bay was evaluated by growth condition and food availability based on a primary production (i.e., monitoring of chlorophyll a concentration).

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 four 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. 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 showed at 23.7 kg per rope indicating that the productivity in 2014 decreased compared to the data in 2013. The amount of chlorophyll a (above 20 m depth) integrated over Ogatsu Bay throughout a year did not differ so much between 2013 and 2014 suggesting the same fluctuation level of the primary production as past. In 2014, the trend of low water temperature was seen in all layers measured (above 20 m depth) in comparison with the data in 2013. By the monitoring results, it seems that the condition with food availability of their farming sites were same fluctuation level between 2013 and 2014. Importantly, the decline of productivity and the stagnation of growth performance in the lower layer were especially seen in 2014 even though the facility numbers in 2014 increased from 2013. This could be caused by competition of food (i.e., phytoplankton) in the lower layer. These results imply that the amount of farmed scallop in 2014 may be overproduction in Ogatsu Bay for the better use of scallop farming with the best growth performance. Currently, we have already collected the data of farmed scallops in 2015 and they are now under the precise analysis.

FY2015 Environmental carrying capacity of cultured scallop in Ogatsu Bay