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Quebec Bulletin
August-September 2015/Volume 18/Number 4

Diving with Blue Whales to Find Out What They Eat!

For the study, a tag is placed on the backs of the blue whales.
For the study, a tag is placed on the backs of the blue whales.

Diving with whales! We can only imagine it, since diving with blue whales or any other marine mammal is prohibited in the St. Lawrence. But this summer, a team of scientists used small electronic devices to do just that, as part of a project to find out where, when and what blue whales in the St. Lawrence eat. Fisheries and Oceans Canada researcher Véronique Lesage is leading this project for a fourth year in collaboration with the Group for Research and Education on Marine Mammals (GREMM) and the Saguenay–St. Lawrence Marine Park.

To follow the whales as they dive, the team of scientists went out on the water twice a week, from June to late August. A tag indicating the depth and time of each mouthful taken by the whale was mounted on the animal's back using a pole or crossbow. The tag, mounted on suction cups, fell off on its own within 24 hours. The team then retrieved it, downloaded the data, and used it again.

While one team monitored the whales' underwater acrobatics and movements, a second team mapped out a grid of the area to identify the types, depth and quantities of food sought by the whales. This information helped Saguenay–St. Lawrence Marine Park experts explain fluctuations in blue whale abundance in this region, and helped Fisheries and Oceans Canada experts determine the type and quantity of food required to reliably attract large numbers of these giants to the waters of the St. Lawrence.

So far, the study has shown that certain species, like the blue whale spend, on average, about 70% of their time feeding. This species also follows the principle of least effort when it feeds, meaning it seeks maximum gain for the least amount of effort. The greater the depth of the food, the more time the blue whale has to spend on feeding itself. The whale compensates for the increased energy expended to reach the food by taking more mouthfuls per dive.

This information is crucial in understanding the feeding bioenergetics of these large predators and the consequences of changes in food resource availability and abundance, and of disruptions caused by whale watching activities.

Mike Hammill

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