Effects of transplant sites and preventive measures against predation on the survival rates of pen shell in the Ariake Sea, Japan

Abstract

: In the Ariake Sea, Japan, pen shells Atrina spp. are an important fishery resource, but now abundance of the stock has decreased. Methods to increase the abundance include transplanting juvenile Atrina spp. in the sea and main-taining the survival rate high. We conducted transplant experiments to compare the survival rates of one genetic lineage of Atrina between 1) transplant sites and 2) preventive measures against predation. We conducted five runs of transplant of Atrina artificial seeds (about 10 cm in shell length) in the inner and outer sea areas, using cages with different mesh opening sizes. We found that 1) Atrina sp. survived better at stations in the outer sea area than in the inner sea area. This trend in the last run was partly explained by a heavy deposition of mud at a station in the inner sea area. 2) Atrina sp. survived better in cages with mesh opening size < 20 mm than those with the size > 20 mm. This was attributed to predatory animals, which presumably include the whelk Rapana venosa , octopi Octopodidae spp., and swimming crabs Charybdis spp. recorded by underwater time-lapse camera. In conclusion, transplant to the outer sea area and protec tion from predators with a mesh < 20 mm opening are promising to increase the survival rate of one genetic lineage of Atrina transplanted in the Ariake Sea.