The marine fishes and invertebrates abundance and composition in the southern Gulf of St. Lawrence (sGSL) has dramatically changed in the last 50 years with a near-extinction of large ground-fish species like the Atlantic Cod (Gadis Morhua), and a rapid increase of invertebrates such as the American Lobster (Homarus americanus). In this project, our goal was to study the changes in occurrence and abundance among the marine fishes and invertebrates found in the sGLS through space and time. To approach this question, we relied on a bottom-trawl survey carried out every September in the sGSL since 1971. For the majority of marine species in this area, this survey provides the only source of information on their abundance and distribution across space and through time. For every survey period temperature, salinity, fluorescence, nutrients, phytoplankton, zooplankton, etc. were also gathered. These explanatory variables provided additional information about the state of the environment and were used to quantify fish and invertebrates’ habitat preferences in the sGSL. To analyze these data we relied on spatiotemporal barrier model. A barrier model considers explicitly physical barriers known to restrain the distribution of organisms, such as islands or the coast in spatiotemporal models.
Results/Conclusions
We tested the influence of the environment through five hypotheses defining the energy, productivity, climatic, habitat constraint and stress mechanisms influencing the distribution of the over 100 species considered. We found that the stress and energy hypotheses were the dominant ones. Surprisingly, climate change was not a dominant factor structuring this group of species except for Arctic species (e.g. Arctic cod (Arctogadusglacialis), Slender eelblenny (Lumpenus fabricii)). We also found that, spatially, the same species used the sGSL differently through the years and this is a recurring pattern for all species considered; fish or invertebrate. Finally, we found that species richness increases almost constantly between 1971 and today suggesting a constant arrival of new species in the sGSL. However, the arrival was not uniform across the sGSL, new species seem to establish in specific areas such as in the Chaleur Bay. In short, a lot of changes have been occurring in the sGSL resulting from ecological and environmental changes but also from political and social decisions that impacted the spatial dynamic of marine species. Understanding these changes will thus help better manage this ecosystem.
