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Krill Visible at the Surface

In areas of strong upwellings along the steep slopes of the St. Lawrence Estuary krill are frequently visible at the surface during daylight hours and often fish feeding on krill can be seen just below the surface. This contradicts the general downward migration of krill in order to avoid intense light. It seems that zooplankton often can’t withstand the strong vertical currents . Capelin fish are also concentrated near or at the surface.

It seems that these strong physical forces concentrate prey densly  enough for efficient feeding so that minke whales do not have to apply any active corralling or entrapment activities prior to a feeding strike. Strictly speaking however, a feeding lunge is  also an entrapment manoeuvre as the whale drives the fish towards the surface concentrating the prey even more.

Feeding Manoeuvres

Feeding manoeuvres are performed at high speed in different body planes but 68% are performed in the dorsal-ventral plane, which is a striking difference to the behaviour found in the Fjord. Strikes right in the water line are called arcs, compared to lunges where the whale‘s body partly leaves the water.

Feeding strikes are characterized by the high speed, expanded grooves and water purging out along the mouth line.

 

The Oblique Lunge

The whale approaches the surface in the dorso-ventral plane with its axis at an angle of ~ 30 to 45° and often a blow is visible.

 

The Vertical Lunge

The whale approaches the surface vertically at or almost at 90° falling back in dorso-ventral plane. Usually the whale takes a blow.

 

 The Lateral Lunge

Similar to an oblique lunge, the whale approaches the surface laterally at about 45°. If it can clear the blowholes high and long enough, it might take a breath.

 

The Ventral Lunge

The whale approaches the surface in ventral plane breaking the surface at about 45°.  As the blowholes are rarely freed it is rather unlikely that the whale can take a breath.

 

The Lateral Arc

During a lateral arc the whale’s body does not break the surface beyond exposing the belly, and/or the tips of a flipper and fluke. Often, it will roll into a dorso-ventral position immediately after the arc in order to breath.

 

The Ventral Arc

Instead of laterally, the whale takes in prey right under the surface in a ventro-dorsal plane. Following the arc, the whale most often rolls back over its right flipper to ventilate right after the strike.