Relationship between instar stages and carapace length of Decapoda, Brachyura, Cheiragonidae the hair crab Erimacrus isenbeckii in the coastal waters of Hokkaido, Japan

The growth characteristics of the hair crab Erimacrus isenbeckii in the coastal waters of Hokkaido, Japan were clarified using an identification method based on external morphology, frequency analysis of carapace length (CL), a mark-recapture sampling protocol, sampling of molted individuals, and rearing experiment. Specifically, the relationship between instar stages and CL was clarified using the former two methods, and to estimate actual growth, a growth formula was derived by applying the initial and post-exuvial CLs of molted individuals that were obtained using the latter three methods to Hiatt's method. There were not large differences between estimations of the CL of each instar by the CL frequency analysis and by the growth formula, so it was considered that both results were reasonable. Since no significant differences were observed between the growth formula results obtained for males after the ninth instar at three sites off Hokkaido, we propose that the growth formula for mature male hair crabs off Hokkaido can be represented as Ln+1=1.035Ln+10.575.