Evaluation of a direct age estimation method for terminally molted male snow crab Chionoecetes opilio (Fabricius 1788) (Decapoda: Brachyura: Oregoniidae)

Recent research suggests that calcified eyestalks and gastric mill ossicles (stomach teeth) can be used to estimate the age of some crustacean species. Along with annual growth of the endocuticle, bipartite bands in the hard tissue are believed to reflect annual growth patterns (similar to fish scales or otoliths) that are retained through repeated molt cycles. Similar bands are observed in the zygocardiac ossicles of the gastric mill from the snow crab (Chionoecetes opilio). If these bands reflect annual growth, they may be used to estimate age, which could enhance understanding growth, mortality, recruitment, and age composition and improve fishery management. While some studies show that the number of bands correlates to other estimates of age for C. opilio, little evidence suggests that bands accumulate annually as growth increments independent of molting. Male C. opilio terminally molt at maturity, after which they can survive for seven years or more. Shell condition, i.e., degree of wear and epibionts on their exoskeleton, is used here and by other carcinologists as a proxy for age subsequent to the terminal molt. We estimated band counts and endocuticle thickness from thin sections of the zygocardiac ossicle of terminally molted male C. opilio across a range of shell conditions from a wild, fished stock. We found no differences in band counts (P = 0.41) or endocuticle thickness (P = 0.13) across varying shell conditions and size. These results do not support the hypothesis that band counts can be used to estimate the age of this species after the terminal molt.