Using an empirical traffic light procedure for monitoring and forecasting in the Gulf of St. Lawrence fishery for the snow crab, Chionoecetes opilio

A traffic light procedure is used for comparing temporal evolution of indicators of the snow crab (Chionoectes opilio) abundance, fishery success and environmental change. Indicators related to recruitment success in the fishery between 1968 and 2003 were followed and comparisons with life history stages (in trawl surveys conducted over 15 years) allowed the temporal sequence of events in the life cycle to be established. Although recruitment seems to be synchronized with bottom temperature, and may be related to abundance changes in groundfish predators, the main factors determining recruitment fluctuations appear to be density-dependent interactions between life history stages. Establishing the abundance and timing of successive life history stages using the traffic light approach seems to provide a reliable indication of their passage through the fishery, and might be used to make forecasts of the condition of the fishery several years ahead. The analysis raises the question of which of a number of possible density-dependent factors are dominant. Two management approaches by reference points and fisheries control rules are suggested.