Research Document 2020/009

Preliminary results from the ecosystemic survey in August 2019 in the Estuary and northern Gulf of St. Lawrence

By Bourdages, H., Brassard, C., Desgagnés, M., Galbraith, P., Gauthier, J., Nozères, C., Scallon-Chouinard, P.-M. and Senay, C.

Abstract

Fisheries and Oceans Canada conducts an annual multidisciplinary survey in the Estuary and northern Gulf of St. Lawrence. The objectives of this survey are varied; assess the biodiversity of species found near the bottom; estimate the abundance of groundfish and invertebrates; assess physical and biological (phytoplankton and zooplankton) oceanographic conditions; monitor the pelagic ecosystem; conduct an inventory of marine mammals, and collect samples for various research projects. In 2019, the survey was conducted between August 13 and September 4 on board the CCGS Teleost. The survey successfully carried out 128 trawl tows as well as 65 CTD water column casts, and 54 zooplankton samples.

This report presents the results from catches from the 128 tows. In total, 79 fish taxa and 208 invertebrate taxa were identified during the mission. Historical perspectives (catch rates, spatial distribution and length frequency) are presented for 25 taxa. These commercial fishery-independent data will be used in several stock assessments including cod (Gadus morhua), redfish (Sebastes spp.), Greenland halibut (Reinhardtius hippoglossoides), Atlantic halibut (Hippoglossus hippoglossus), witch flounder (Glyptocephalus cynoglossus) and northern shrimp (Pandalus borealis).

A preliminary analysis of water temperature data collected in 2019 shows that conditions have warmed at 150 m and deeper, reaching new records since 1915 at 250 and 300 m. The surface water and cold intermediate layer temperatures were near normal in August.

The ecosystem of the northern Gulf of St. Lawrence is currently undergoing major changes in the composition of the demersal species that are present there. The Atlantic redfish (Sebastes mentella) is making a strong comeback in channels of the Gulf of St. Lawrence, alone, it constituted more than 85% of the catches made during the survey. In addition, species that are found more frequently outside the Gulf of St. Lawrence and associated with warmer waters, were also caught frequently in this summer survey such as silver hake (Merluccius bilinearis), Atlantic argentine (Argentina silus) and northern shortfin squid (Illex illecebrosus). On the other hand, species associated with cold waters, such as northern shrimp and Greenland halibut, have been declining for more than a decade.

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