Estimating The Sources Of Pen Shell Atrina Spp. Larvae In Ariake Sea, Japan

Pen shell,Atrina spp.is an important marine product at the head of Ariake Sea,but its catch amount has drastically decreased in the past 30 years,so that the recovery of the catch is an urgent task.The recent decrease of pen shells may be caused by decrease of the larvae supply from the adult pen shells.For the recovery of the shells,the sources which can supply larvae to the head of Ariake Sea should be protected or developed.In this study,we estimated the population of such adult pen shells by using numerical simulations with particle tracking method.First,we estimated the spawning period,i.e.,the particle-release period,from observation data of the lengths of young settling shell on the seabed and the larvae in water column around the head of Ariake Sea.The numerical model used in the present study was the finite volume community ocean model,i.e.,FVCOM,in which unstructured triangular grids are adopted.Using this model,we reproduced the flow fields during the suspended period of the larvae with high accuracy.Finally,we coupled the calculated flow fields with the particle tracking method to estimate the larval sources of pen shells.As a result,we simulated the larval transport process,and revealed that the adult pen shell population off the coast of Shimabara is closely connected with high larvae supply to the head of Ariake Sea.Therefore,the adult pen shells in this region should be protected to recover the catch amount of pen shells,Atrina spp.at the head area of Ariake Sea.