Stock assessment and stock status of the Japanese mantis shrimp Oratosquilla oratoria in the Buzen Sea, Seto Inland Sea, Japan

A stock assessment of Japanese mantis shrimp Oratosquilla oratoria was conducted using research data sampled by small trawl vessel in the Buzen Sea, Seto Inland Sea, Japan, from 2007 to 2009. The fishing mortality coefficient estimated for every half-year from the 2007 year class suggested that the reduction of population by discard began soon after recruitment. The survival rate after one year of recruitment was estimated as 13.4%. The reduction of individuals before growing to the minimum landing size was large. The yield per recruit and spawning per recruit analyses show that to increase both catch and egg production, reduction of fishing effort until two years after settlement is effective. It is particularly important to reduce the fishing effort during the next summer after settling which includes high discard mortality.