Distribution and habitat selection of early benthic stages of snow crab Chionoecetes opilio

Early benthic stages of the snow crab Chionoecetes opilio are presumed to be very stenothermic; they may be sensitive to environmental changes and thus affect subsequent adult population abundance. Little quantitative information exists on the habitat preferences of juvenile snow crabs to verify this. We determined the distribution pattern of juveniles in the NW Gulf of St. Lawrence, Canada, in May 2001. Temperature and substratum preferences were evaluated through controlled laboratory experiments in aquaria that had a temperature gradient and offered a choice of 3 sediment types (mud, sand and gravel). In general, early benthic stages displayed sharp size-/agedependent distributions and habitat preferences. In the field, juveniles from Instars I to IV were scarce in the core of the cold intermediate layer (CIL) but present immediately above and below this layer, where temperatures were > 0C. Older juveniles (Instars VI to VIII) were concentrated at depths < 27 m above the CIL. An analysis of historical data from 1989 to 2000 supported this depthdistribution pattern. Temperature preference in the laboratory shifted from a cold (0.0 to 1.5C) to a warmer temperature range (1.0 to 4.5C) between Instars III and V. Juveniles preferred mud in general. Early juvenile instars could represent the weakest link in the snow crab's life cycle because of their narrow habitat requirements.