Why do certain species of seal swim on their backs?

It all depends on the season. In winter, from late February to mid-March, the harp seal is in its breeding season in the St. Lawrence River. Like many other seal species, they mate in the water. They are therefore particularly vulnerable and must remain alert to any activity that could harm them (disturbance, threats) or benefit them (food). Since females can give birth to only one pup per year, their reproductive success is particularly important.

In the summer, the harp seal migrates to the waters of the Canadian Arctic or Greenland. In these regions, monitoring the marine environment is even more critical than in the St. Lawrence River due to certain predators lurking there: killer whales, sharks, or even walruses, depending on the location. “Most of these predators could emerge from the depths, so keeping an eye on what’s below is more important than watching what’s happening above,” says Mike Hammill. However, the researcher notes that swimming on its back could potentially put the harp seal at a disadvantage when facing a land-based predator such as the polar bear, which tends to emerge from the sea ice.

This behavior will need to be studied in greater depth to understand what drives the harp seal to scan the seafloor, or how this posture affects its swimming. Certainly, this characteristic makes the seal easier to distinguish from other pinniped species found in the St. Lawrence Estuary. Or, at times, it makes it easier to mistake it for a beluga when viewed from the sky!