Getting to Know the Herring of the St. Lawrence Upper Estuary, a Beluga Prey

This project, which began last year, focuses in particular on the spawning grounds of this small silver fish. Herring migrate from the Gulf to the Estuary to spawn in spring and fall. This represents an important food source in spring for female belugas that are pregnant at that time of the year. However, since the early 2000s, a decline in the spring herring population coming from Chaleur Bay has been observed.

This is the master’s thesis topic of Laurence Lévesque, student at the Université du Québec à Rimouski (UQAR), in collaboration with Parks Canada, ISMER, MLI-DFO, and MDDELCC.
From late May through the end of June, on board L’Alliance, herring larvae were sampled twice a week in the areas of Île Verte and Île aux Lièvres.

The second part of the study, which began on July 10 and will continue through September at a rate of twice a week every three weeks, consists of determining whether the retention zones (places favourable for the concentration of larvae depending on environmental and physical conditions, including temperature) are conducive to larval growth of herring. This part of the study will be carried out on board Le Krill (DFO), notably in the areas of Île Verte, Île aux Lièvres, Rivière-du-Loup, Baie des Rochers and La Malbaie.

Some results from last year

Larval abundance of herring in spring is still very high and is greater than that of the fall cohort. The spring cohort that comes to spawn in the Upper Estuary does not seem to be affected like that of Chaleur Bay, or at least not as much. More specifically, there are approximately 800 larvae per 100 cubic metres of water (800/100 m³) on the Batture aux Pèlerins and the South Channel as well as high abundance around Île aux Lièvres, Île Blanche and Île Verte. In the fall, figures of 300 larvae / 100 m³ are found mainly in the South Channel and the Batture aux Pèlerins. Retention areas are mostly found in the South Channel and the Batture au Pèlerins, as we sampled larvae of all sizes in these locations, suggesting that older larvae remain there to grow.

Also, different cohorts were identified by their size (older larvae are necessarily larger at some point in time). There are six cohorts that hatched during the summer of 2014. The summer cohorts, although of quite low abundance, are present and significant, which was not observed in the studies conducted in the 1980s and 90s.

A number of pieces of the puzzle remain to be completed: physical condition of the larvae, stomach content, statistical analysis to correlate growing conditions to environmental data, etc.