Growth after recruitment completion and life span of the Japanese mantis shrimp Oratosquilla oratoria in Tokyo bay [Japan]

Abstract

Mean body lengths of age groups by sex of the Japanese mantis shrimp Oratosquilla oratoria in Tokyo Bay were determined by 2, 423 females and 2, 293 males using size-frequency analysis method. A growth curve was fitted to length at age data and the life span was examined. It was found that the recruitment period started in November with a body length around 5cm and com-pleted in June of the following year. The mode of age O group during the recruitment period was not used in further interpretations, because the continuous addition of newly recruited individuals was found to lower its value. After recruitment completion, it was found that the growth of the mantis shrimp has seasonal oscillation with the highest growth rate from late summer to late autumn. Females showed higher growth oscillation than males. Growth of the mantis shrimp was best expressed by the Pauly and Gaschutz equation as Lt=16.12{1-exp[-0.395(t+2.667)-(0.486/2π)sin 2π(t-0.323)]} for females and Lt=21.51{1-exp[-0.264(1+2.473)-(0.232/2π)sin 2π(t-0.281)]}for males, where Lt is body length in cm and t is age in months. It seems that most of the mantis shrimp in Tokyo Bay died during age 2.