Chouinard, P-M., and Dutil, J-D. 2011. The structure of demersal fish assemblages in a cold, highly stratified environment. – ICES Journal of Marine Science, 68: 1896–1908. Fish are a major component of marine ecosystems, with many species co-occuring in the same habitats. Potential interactions among species and with the environment can be studied through the identification of species assemblages. Data from bottom trawl surveys (2004–2008) conducted in the estuary and northern Gulf of St Lawrence were analysed using multivariate methods (cluster, multidimensional scaling, and detrended canonical correspondence analysis) to describe the structure and composition of demersal fish assemblages, including rare and smaller non-commercial species. The spatial variability in environmental conditions that characterizes the study area has a significant impact on the composition of fish assemblages in the region. In all, 35 taxa were classified as key, and 6 main fish assemblages were described, based on catch in numbers. These assemblages had a coherent spatial distribution in the study area, associated with either depth, salinity and temperature, or dissolved oxygen. The analyses showed overall strong correlations between species abundance and prevalent environmental conditions and explained 18.4% of the variance in species abundance data and 79.2% of the variance in the species–environment relationship.

This study examines the spatial distribution of three species of wolffish in the Gulf of St. Lawrence on the basis of trawl surveys.A standardized method is proposed to assess species–habitat associations for the purpose of management and recovery of endangered marine species.Catch data (presence/absence in trawl sets) and landscape and environmental characteristics of the sea floor were aggregated using a common grid (100 km2 cells), and species–habitat relationships were explored using geospatial tools.Relative occurrence was lower and area of occupancy and concentration were much smaller for the northern wolffish (Anarhichas denticulatus) than for the spotted wolffish (Anarhichas minor), with the striped wolffish (Anarhichas lupus) being most widespread. Significant relationships were observed between values of the local spatial autocorrelation Gi* statistic and habitat descriptors for each of the three species.Hot spots for spotted and striped wolffish occurred in areas where a greater diversity of relief and habitats was found. They were associated with intermediate depths, coarse sediments and rock outcrops, and lower salinities and temperatures than for northern wolffish.Northern wolffish appeared to be associated mainly with the deep water sloped habitat bordering deep channels, whereas spotted and striped wolffish both concentrated most intensively into neighbouring deep water shelf habitats and relatively cold shallow to mid‐depth shelf habitats of the northern Gulf.The RDA analysis indicated a significant relationship between Gi* scores of the three species and environmental variables. The model explained 52% of the variability in the data; northern wolffish showed a distinct relationship compared with the two other species.The conservation of marine species and protection of their habitats pose a major challenge given the limited amount of information typically available on rare species and the scale and complexity of marine processes that affect those species. The broad‐scale approach presented here allows the provision of advice on important habitats on the basis of the best available knowledge. Copyright © 2013 Her Majesty the Queen in Right of Canada

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