This text is part of the special section Relève en recherche
If Quebec’s northern shrimp delights gourmets, there is a “fine palate” that could end up endangering it: redfish. Now over-represented in the waters of the Gulf of St. Lawrence, this predator has a diet that is rather worrying for the future of the delicate crustacean. This is highlighted by the work of Sarah Brown-Vuillemin, doctoral student in oceanography and winner of the latest Acfas research popularization competition.
“More and more shrimp are found in the stomach contents of rockfish larger than 25 to 30 cm. This can be quite worrying because the proportions of predated shrimp are huge. The redfish manage to find the zones where the shrimp are found in greatest abundance, and it predates in particular the northern shrimp which is a species of high commercial value for Quebec ”, underlines Sarah Brown-Vuillemin, doctoral student at the University. of Quebec in Rimouski (UQAR).
As part of her thesis, the researcher analyzed – with the help of other colleagues – the stomach contents of nearly 7,000 rockfish collected during Fisheries and Oceans Canada oceanographic missions carried out in the 1990s and 2010s. .
While the small rockfish of the first period reveled in zooplankton associated with cold water, the baby rockfish of the more recent period also ate zooplankton, but of another species, this time more associated with warm waters, the global warming having done its work in the meantime.
In adult rockfish, on the other hand, the attraction to shrimp is similar for both periods. Because even if the large redfishes of yesterday and today also feed on fish – capelin for the first period studied, and small redfish for the second – shrimp remains “the predominant category in the diet of ‘a large redfish,’ says Sarah Brown-Vuillemin.
Extra pressure on the shrimp
The predation of large rockfish on northern shrimp is of concern, since the latter are already facing multiple difficulties. “There are environmental parameters that already have an impact on the species, such as hypoxia – the decrease in oxygenation in water bodies – due to global warming, and which is increasingly intense in the waters. from the Gulf of St. Lawrence. In addition to that, we have other predators in the system that also feed on shrimp, ”argues Mme Brown-Vuillemin.
In the opinion of the doctoral student, her results reflect the need to continue exploring this issue. “It is very important to have a follow-up over time, of the consumption of shrimp, to see how it evolves. This will make it possible to provide as much data as possible that can help managers put in place questions or solutions on the fate of shrimp, but also of redfish, ”she believes.
A passion for predatory relationships
Awarded for the presentation of this study at the last research popularization competition of the Association pour le savoir francophone (Acfas), Sarah Brown-Vuillemin has always been passionate about marine biology themes relating to prey-predator relationships.
“During my university studies, I always did internships on the study of the diets of large fish, rays, large predators. At the end of my masters, I took a break and went to live in New Zealand for a little over a year, just to travel. When I returned to France, I knew that I wanted to be a marine biologist ”, relates the young woman from the city of Toulon, not far from Marseille, in the south of the country.
It was then that Mme Brown-Vuillemin got in touch with the one who would become its research director – Dominique Robert, from the Institut des sciences de la mer de Rimouski (ISMER) – who was just looking, at the same time, for a doctoral student to work on the diet of redfish. “I said to myself that it would be a great opportunity for me to continue in this direction and to specialize even more in the notions of trophic networks”, indicates the student.
According to the researcher, the study of diets is as fascinating as it is preponderant, as it constitutes a mine of precious information. “This allows us to understand how an ecosystem works, how species are united among themselves, and their optimal conditions for living in an environment. This is what pleases me. We can thus affect different ecological groups: redfish, but also zooplankton, shrimp, etc. It’s very stimulating from a scientific point of view, ”she argues.
And this knowledge takes on all its meaning, at a time when the challenges are sizeable.
“Marine ecosystems are under great pressure, especially human ones. To provide solutions and restore healthy ecosystems, we therefore need to fundamentally understand what is happening there, ”concludes the doctoral student.