A length-based population analysis (LPA) was applied to the Eastern Hokkaido hair crab Erimacrus isenbeckii, incorporating stochastic growth and gradual recruitment over length. A nonlinear least squares approach was used to estimate growth, probability of molting, abundance, and recruitment. The model was applied to abundance and catch data from 1992 to 1997. The estimated population abundances by LPA fit observed abundances well. This suggests that the LPA model can describe the population dynamics of hair crab in Eastern Hokkaido. Furthermore, the LPA model may apply to other populations of unknown age structure like the hair crab in this study. Estimated abundances and recruitments show that the hair crab population in Eastern Hokkaido is strongly influenced by yearly recruitment. A large abundance is the result of abundant recruitment. It may be caused by the unsettled condition of the hair crab population in Eastern Hokkaido.
LPA can estimate yearly recruitment. It makes possible clearly indicating the reference point such as YPR or SPR. It can ensure that effective stock management of hair crabs in Eastern Hokkaido is realized.