Fin whales from the Gulf of St Lawrence

Fin whales are a large species of whale, which behaviour and stocks are still uncertain. Tracking them using Argos telemetry tags enables to better assess those, and thus better protect the species.

Fin whales (Balenoptera physalus) are the second largest baleen whale species, after the blue whales. They are found in almost every ocean out of the tropics. Their seasonal movements are believed to be similar to those of other baleen whale species (i.e. large-scale north-south seasonal movements of most individuals between high latitudes for foraging in summer, lower latitudes for breeding and calving in winter), but no breeding or nursing ground have been identified. Moreover, their stock structure definition is uncertain, possibly outdated, as it is based on morphological measurements from whaling and captures of tagged whales from the past hundred years or more. Satellite telemetry can help in a better understanding of both questions.

Tracking with satellite telemetry

Argos satellite transmitters were fitted on twenty-eight individual fin whales: eight in the Gulf of St Lawrence during the summer and 20 in the Estuary during the fall. The tags transmitted locations for 7 to 115 days, with distance covered ranging from 36 km to 6,993 km (mean 1,300 km, median 681 km). A model was applied on the locations to discriminate between foraging and transit movements, in particular. Comparisons with environmental data (sea surface temperature) was also made.

Overall, the transit behaviours were more frequent in winter (28%). In summer 92% behaviours were for the “area-restricted-search”, a kind of tortuous movement which often corresponds to foraging but can also be possibly socializing (including breeding), etc. The migration patterns were highly variable in timing, extent, and destination depending on the individuals, though. Of the 20 fin whales tagged in in the Estuary during the fall, the 8 still tracked in winter exited the Gulf of St Lawrence towards South. Two went back to the Estuary afterwards. Even the destination does not seem common in winter (though water temperatures above 22°C seems to be), which raises further doubts about breeding grounds being their

Several of the tracked fin whales went to the Scotian Shelf, including part of the Gulf of Maine, thus suggesting that this area is an important wintering ground for fin whales summering in the Gulf of St Lawrence. The whales exhibited area-restricted-search behavior there, though, outside their traditional feeding season. The whales which went much farther south almost constantly exhibited transit behaviors.

None of the tracked whales moved into the eastern Gulf of St. Lawrence or Newfoundland and Labrador waters, which may indicate that the fin whales there are from a separate stock.

The persistence of fin whales in a small area in the Estuary for several weeks /months late fall early January, the short trips out with a return to the tagging site may be explained by food supply limited to a few areas only within the Gulf of St Lawrence. This could be a consequence of recent warming conditions, since record warming was observed each year for the Estuary and Gulf of St Lawrence till 2010. It has been shown that fin whales are arriving one month earlier than about 30 years ago, due to sea ice loss, and departing two weeks later (in average). This could have an impact on migration, either limiting the need to migrate, or limiting the food supply and thus the energy stored before migration or forcing the whales to go further out of their usual feeding grounds. The high variability of behaviors observed within the species suggests that the species could prove resilient to those changes, though.

Reference and links

• Ramp, C., Lesage, V., Ollier, A. et al. Migratory movements of fin whales from the Gulf of St. Lawrence challenge our understanding of the Northwest Atlantic stock structure. Sci Rep 14, 11472 (2024). https://doi.org/10.1038/s41598-024-62173-1
• Aquatic species at risk, DFO https://www.dfo-mpo.gc.ca/species-especes/sara-lep/index-eng.html