Instar identification and life history aspects of juvenile deepwater spider crabs, Chionoecetes tanneri Rathbun

For the deepwater spider crab, Chionoecetes tanneri , seven instars from first crab stage (3.8 mm carapace width (CW)) to instar VII (26.8 mm CW) are identified from size-frequency histograms. The average growth per molt for the first seven instars is 39% and the time from egg to instar VII is estimated to be 20 months. Measurements of chela length, abdomen width and carapace width were used to define two growth phases for C. tanneri and to determine size at maturity for males (142.7 mm CW) and females (102.3 mm CW). The unequal sex ratio of adults (29% males) and presence of chitinoclastic lesions on 76% of the adults females as compared with only 29% of the adult males suggest that adult females are anecdysic. In this study of material collected off the southern Oregon coast, the mean adult carapace widths for males and females is very close to the sizes reported for adult males and females (148.9 and 102.5 mm CW respectively) from the northern Oregon coast.