Drivers of Recruitment in a Key Marine Invertebrate: Investigating Early Life Stages in Snow Crab

Snow crab landings in the Gulf of St. Lawrence (eastern Canada) have fluctuated greatly since the beginning of the fishery due to highly variable recruitment. This variability is established early in life and may result from bottom-up processes related to climate variation, top-down effects and/or population-intrinsic processes. We explored how climate, larval production, intercohort cannibalism and groundfish predation may have affected recruitment of snow crab in the northwest Gulf of St. Lawrence over the period 1989‒2012. Abundance of early juvenile snow crabs (3‒25 mm carapace width), representing the first three years of benthic life, came from an annual trawl survey and was used to determine year-class strength (YCS). Larval production and surface water temperature during the planktonic phase were the two main factors determining YCS up to about 8‒9 months after settlement time. The population structure set by larval supply to the benthos was progressively modified by intercohort cannibalism and bottom water temperature effects. Cannibalism was the most important factor affecting YCS after three years of life and appears to be a strong driver of snow crab recruitment variability. The findings suggest that climatic and population-intrinsic processes are more important than top-down effects in determining snow crab recruitment.