What do St. Lawrence belugas eat?

Updating this knowledge is not as straightforward as it might seem. Like any cetacean, the beluga is difficult to track during dives and documenting its feeding sequences in the murky waters of the St. Lawrence or Saguenay is challenging. And, other than a few rare occasions when prey is seen in a surfacing beluga’s mouth, these animals show little of their menu. Scientists must therefore rely primarily on the stomach and intestinal contents of dead animals.

Results show that the St. Lawrence beluga has a varied diet that consists of fish and invertebrates generally measuring less than 30 cm. The most frequently found prey are bottom-dwelling fish such as cod, hake and redfish, as well as polychaetes (bristle worms) and small cephalopods such as squid. Other fish including smelt or eel are occasionally found, as are marine invertebrates (shrimp, gastropods, etc.).

These conclusions differ somewhat compared to previous knowledge. In the 1930s, the prey most commonly found in beluga stomachs were sand lance and capelin, fish that are still found in their diet today, but less frequently.

“Redfish, American eel and two species of hake [are] present in the contemporary beluga diet, but were not detected [in the past]. The opposite has been observed for Atlantic salmon, Atlantic sturgeon, sea lamprey, haddock and rays,” reports the recent study.

Analyzing the stomach contents in beluga carcasses also makes it possible to note seasonal variations, as well as differences in diet between males and females, particularly in summer: “Sand lance as well as eel, rainbow smelt and Atlantic herring were detected in the beluga diet exclusively in late summer and fall, while other species […] were detected in spring or fall,” writes Véronique Lesage. These variations are attributed to the seasonal availability of prey as well as the movements of belugas.

It is known that male and female belugas use the multiple habitats of the St. Lawrence differently. Logically, this gender segregation leads to differences in diet. For example, fish living near the sea floor are present year round in the stomachs of males, but appear to make up part of the females’ diet only in spring and fall.