Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

In the northern Gulf of St. Lawrence (nGSL), redfish (Sebastesmentella and S. fasciatus combined) are at record levels of abundance following the strong recruitment of three consecutive cohorts in 2011–2013 and have become by far the most abundant demersal fish in the region. Understanding redfish trophic relationships is essential for the effective management and conservation of speciesin the nGSL ecosystem. To date, description and quantification of redfish diet in the region have been restricted to conventional stomach contents analyses (SCA). Using analysis of fatty acid (FA)profiles as complementary dietary tracers, we conducted multivariate analyses on 350 livers of redfish which were collected in combinaison with stomach contents during a bottom-trawl scientific survey in August 2017. The predator FA profiles were compared to those of eight different redfish prey types identified as dietary important with SCA. Results suggested similitude between SCA and FA results, with zooplankton prey being more related to small (< 20 cm) and medium (20–30 cm) redfish (16:1n7, 20:1n?, 22:1n9 and 20:5n3) than large(≥ 30 cm) ones while shrimp prey seemed more related to large redfish size classes (18:2n6 and 22:6n3) relative to the small and medium ones. While the SCA offers a glimpse in the diet only based on the most recently consumed prey, analysis of FA profiles provide a mid-term view indicating pelagic zooplankton consumption on calanoid copepod and confirming high predation pressure on shrimp. This studyconstitutes the first attempt of combining FA with SCA to assess the diet of redfish, highlights the benefits of FA as a qualitative tool and suggests improvements for future studies.