BUI, A.O.V., M. CASTONGUAY, P. OUELLET, J.-M SÉVIGNY, 2011. Searching for Atlantic Cod (Gadus morhua) spawning sites in the northwest Gulf of St Lawrence (Canada) using molecular techniques. ICES J. Mar. Sci., 68(5): 911-918.

[Résumé disponible seulement en anglais]
The overexploitation of Atlantic cod (Gadus morhua) in the Northwest Atlantic led to the collapse of most stocks and the demise of spawning components in the early 1990s. In the northern Gulf of St Lawrence, the spawning component of Northwest Atlantic Fishery Organization Division 4S was believed no longer to exist after the collapse. To verify this hypothesis, we used molecular techniques to identify cod, haddock, and witch flounder (CHW) eggs precisely, in an attempt to locate the potential remaining spawning sites for cod in the northwest Gulf. Ichthyoplankton surveys were conducted in spring from 2005 to 2008. Results were compared with those of surveys that took place in spring in the same area 20 years earlier to determine if there had been any changes in spawning location and egg abundance. Atlantic cod made up the majority (97 %) of CHW eggs identified. The presence of stage I cod eggs proved that there is still a cod spawning component in the northwest Gulf of St Lawrence, but egg abundance has declined by about an order of magnitude compared with the 1980s. There was no obvious difference in the location of cod spawning grounds between the two decades

BUI, A.O.V., P. OUELLET, M. CASTONGUAY, J.-C. BRÊTHES, 2010. Ichthyoplankton community structure in the northwest Gulf of St. Lawrence (Canada) : past and present. Mar. Ecol. Prog. Ser., 412: 189-205 .

[Résumé disponible seulement en anglais]
Biodiversity can play an important role in the stability and resilience of ecosystems when these are faced with environmental change or anthropogenic impacts. Historically, the northwest Gulf of St. Lawrence had high fish egg and larval productivity. To assess changes in the ichthyoplankton community of this region, data from sampling surveys that were carried out in spring from 1985 to 1987 were compared with data from spring 2005 to 2007. Significant differences in ichthyoplankton abundances between the 2 decades and sampling times (May versus June) were revealed by multivariate analyses (nMDS, ANOSIM, PERMANOVA, and SIMPER) and univariate (ANOVA) analyses. Total ichthyoplankton abundance was lower in the 2000s than during the mid- 1980s. Although larval sandlance Ammodytes spp. abundances did not change significantly, other taxa, such as Stichaeidae larvae and H4B eggs (gadids and merlucciid hakes, rocklings, butterfish Peprilus triancanthus, windowpane Scophthalmus aquosus and Gulf Stream flounder Citharichthys arctifrons), became more abundant; the abundance of CHW eggs (cod Gadus morhua, haddock Melanogrammus aeglefinus, witch flounder Glyptocephalus cynoglossus), and redfish Sebastes spp. larvae generally declined by more than an order of magnitude. Greenland halibut Reinhardtius hippoglossoides larvae also appeared in the 2000s assemblages. This dominance shift in the ichthyoplankton community reflects the demise of large fish predators and the response of the non-commercial species. Our study provides much-needed new information concerning current biodiversity and productivity of the fish community in the Gulf of St. Lawrence and insights into changes influenced by groundfish collapse and environmental fluctuations.©2010 Inter-Research