What can we learn from research on St. Lawrence seals?

For 20 years now, the QMMERN has been working with dead or distressed marine mammals in Quebec. At the same time, DFO scientists have been studying pinnipeds – including harbour seals and grey seals in the Gulf of St. Lawrence and its estuary – for the past few decades. Through multidisciplinary programs, the MLI research team aims to better understand the reproductive status, diet, age of individuals, and causes of mortality in these two species. In recent years, DFO and QMMERN have partnered together to collect data.

Xavier Bordeleau is unequivocal: The QMMERN plays a vital role in pinniped research!

Indeed, if conditions allow, seal carcasses recovered by QMMERN are taken to the Faculty of Veterinary Medicine in Saint-Hyacinthe, and a necropsy is performed by an expert team from Université de Montréal. If the carcasses cannot be recovered, data and samples can be collected directly in the field by QMMERN’s volunteers, mobile teams or satellite teams. These samples and necropsies are a gold mine for the advancement of pinniped science!

By examining a seal’s teeth, it is possible to assess the animal’s age, much in the same way that growth rings are used to determine the age of a tree. Xavier Bordeleau explains that the teeth sampled by QMMERN are amongst the only data that allow DFO to determine the true age of seals in the estuary and gulf! The study of QMMERN-recovered carcasses also helps better understand seal mortality and determine the most common causes thereof in newborns and adults. Necropsies can also provide diet-related data, particularly by examining the contents of the seals’ intestines and stomachs.

Thanks to field data obtained by QMMERN as well as research conducted by MLI, a new cause of grey seal mortality has been reported: predation by great white sharks.

Over the past two years, DFO has documented 80 interactions between great white sharks and grey seals. Xavier Bordeleau explains that their large population (over 350,000 individuals!) could explain why grey seals are more affected than other species, although one or two cases involving harbour seals have also been recorded. The overlap between grey seal and great white shark habitats could also explain the high number of predation cases on the species.

In 2024, 15 great whites were tagged by MLI. Nine individuals were captured in 2023. The tags placed on these huge fish allow us to track their movements and better understand their interactions with grey seals. Images of the sharks are also used to help determine which individuals are frequenting the gulf through photo-identification. Much like whales, sharks have pigmentation patterns and variable dorsal fin profiles that allow us to distinguish them from one another.

Currently, no data are available on the true abundance of great whites in the gulf, but their presence raises many questions, explains Xavier Bordeleau. What is their role in the ecosystem? How will their abundance influence seal distribution? The valuable seal data collected by DFO and QMMERN give scientists hope for answers.

Through rigorous surveys, Xavier Bordeleau and his scientific colleagues at MLI are closely monitoring variations in the abundance of seal populations in the eastern Atlantic. For researchers, these fluctuations are valuable indicators for studying the impact of climate change on ecosystems. Variations in seal dispersal and abundance may also enable scientists to assess the pressure that pinnipeds are putting on prey and fish stocks.

The most recent estimate for harbour seals, a species not currently at risk, was around 25,000 individuals in eastern Canada. This species was once more abundant, but due to hunting, which ended in the 1970s, the population has suffered a decline. A new report presenting the results of harbour seal surveys is expected to be published soon, according to Bordeleau.

Frequently observed in the St. Lawrence (in addition to grey and harbour seals), harp seals are estimated to number nearly 4.5 million in eastern Canada. Despite this high figure, the population is currently facing a number of challenges that are pushing it toward a possible decline, particularly the decrease in pack ice, which is essential for pupping females.

Long-term monitoring of pinniped populations helps us to better understand them and make informed decisions on how to manage them and ensure a better coexistence. Seals are “charismatic species that are part of the ecosystems; we must ensure that they stay healthy,” concludes Xavier Bordeleau.