Research Document 1998/38

Possible effects of changes in CIL temperature and thickness on population dynamics of snow crab, Chionoecetes opilio, in the Gulf of Saint Lawrence

By B. Sainte-Marie and D. Gilbert

Abstract

The cold intermediate layer (CIL) of the Gulf of Saint Lawrence is subject to interannual changes in core temperature and thickness, which are superimposed on persistent west-east and north-south gradients for these same variables. Since the mid 1980's, the CIL has been thicker and colder than normal. This cold period has lasted for more than one generation of snow crab (Chionoecetes opilio) and may have had major effects on the spatial distribution and population dynamics of this species. The extent of the spatial distribution of snow crab apparently increased during the cold period, while egg production may have declined owing to a shift from a 1 year to a 2 year duration for egg incubation. Furthermore, we propose that the size threshold for the onset of gonad development and the size at terminal molt in both sexes are partly temperature-dependent. Cohorts with immature individuals subjected to the recent cold period are currently expressing precocious maturity, and a large fraction of males are undergoing terminal molt to sublegal sizes. These changes may have important consequences for reproductive processes and may directly affect fishery performance in the next years.

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