Spatial dynamics of female snow crab (Chionoecetes opilio) in the eastern Bering Sea

Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Based on preliminary information, we hypothesized that females undergo an extensive ontogenetic migration, tracking down environmental gradients. We analyzed a 25-year time series of survey data and defined ontogenetic stages in terms of a shell condition index calibrated with radiochemical methods. Pseudo-cohorts of mature females (groups of females that undergo puberty molt in a given year) recruit to the mature female pool in the Middle Domain (50-100 m) of the intermediate shelf. Females undergo puberty molt and primiparous mating in winter. Over the next year, they migrate an average net distance of 73.5 nautical miles towards the shelf edge following a predominantly northeast-southwest direction. Maximum post-terminal molt life span is 6-7 years. Results support the hypothesis that the variable tracked is near-bottom temperature. Although near-bottom temperature fields vary from year to year, the corresponding vector field is a conservative template, which explains the consistency observed in the pattern of migration. Elucidation of the life history schedule of mature female snow crabs in the eastern Bering Sea revealed that it is very similar to that reported for eastern Canada, although patterns of migration may differ substantially between the two systems.