Population Dynamics of the Mud Shrimp Upogebia major (de Haan), a Burrowing Pest in Clam Beds from Seonjae-Do Tidal Flat, Korea

초록

Recently, the mud shrimp Upogebia major has occurred in high abundance in many of the tidal flats along the west coast of Korea, posing a serious threat to the Korean clam industry. We report here the growth, mortality, recruitment and production of U. major in Seonjae-Do Tidal Flat (lat. 37°14’N), where the shrimp suddenly settled in 2010. Shrimps were collected monthly during low tide and a circle of 5m2 was excavated to 80–100cm below the surface sediment from February 2012 to June 2014. The burrow densities were also estimated at the same time using a quadrate. A total of 7,383 individuals were sampled and their carapace lengths were measured. The population structure differed significantly between males and females. Specifically, the monthly mean sex proportion was 1.27, with males usually outnumbering females. Growth functions for carapace length estimated from the modified von Bertalanffy growth model showed that: CLt(mm)=37.68[1-exp[-0.30(t+0.196)-(0.84X0.30/2π)(sin2π(t-0.81)-sin2π(-0.196-0.81))]] CLt(mm)=37.38[1-exp[-0.30(t+0.185)-(0.90X0.30/2π)(sin2π(t-0.84)-sin2π(-0.185-0.84))]] CLt(mm)=38.80[1-exp[-0.27(t+0.185)-(0.98X0.27/2π)(sin2π(t-0.87)-sin2π(-0.185-0.87))]] when sexes were pooled, for males and females, respectively. The amplitude of seasonal growth oscillation (C) was 0.84, 0.90 and 0.98, respectively. The winter point estimated by ELEFAN in FISAT2 was 0.79, 0.82 and 0.85, respectively. These results showed a clear seasonal growth pattern with a slowdown around mid-October to early November. According to the estimated growth coefficient of the von Bertalanffy growth function, the mud shrimp population in Seonjae-Do grows until a carapace length (CL) of 12mm after settlement for a year, after which another two and a half years are required to attain 25mm in carapace length for spawning. Ovigerous females were collected between November and April and settled juveniles were found in June in 2013 and 2014, but those coh