Gliding or stroking?

August 20 – One of the first things we discover with the accelerometer instruments is that narwhals swim differently when they try to move away from humans or sounds.  During normal dives narwhals save energy by changing between periods of swimming and gliding. Called burst-and-glide swimming, marine mammals like narwhals take advantage of their streamlined shape to move quickly through water using the minimum number of strokes and simply slipping along on a glide. Typically, narwhals take six or seven strokes (shown by the big spikes in the pink area of the above graph) and then glide for 30-60 seconds. Then they repeat the process. Just like taking fewer steps costs you less energy during a day, taking fewer strokes allow the narwhals to save energy.  Reducing the amount of energy to swim means that the narwhals can conserve their oxygen. This is especially important when they are holding their breath during a dive, and this special swimming gait allows narwhals to dive longer.

This all changes when narwhals swim away from a disturbance.  In the example below, Bjarne, one of our male narwhals hears a boat pass by. Suddenly, he swims as fast as he can using big swimming strokes. He never glides. Although this enables him to escape the noise quickly, this is a very expensive way to swim. As a result, he may need to shorten the length of his dive. 

Our team now wonders, if Bjarne reacts so strongly to a small boat passing nearby, how will be react to  bigger ships or louder noises?