How Do the Ventral Grooves of Rorquals Function?

The word “rorqual” comes from the Norwegian rorkval, which means “tubed” or “furrow-bellied” whale. The name refers to the folds that line a whale’s throat from under its mouth to its stomach. These folds, which resemble expandable concave furrows in shape, have the peculiarity of stretching like an accordion.

When rorquals locate a school of krill or small fish, they accelerate and, at the last second, open their mouth. The mandible (lower jaw) then opens to 90°, allowing water and prey to enter, after which the stomach balloons like a parachute. The volume of water engulfed is sometimes greater than the volume of the rorqual itself. The ventral pouch expands by 162% in girth and 38% in length. The water is then expelled through the half open mouth by means of the powerful muscles of the belly and tongue, which push it through the baleen attached to the maxilla, or upper jaw bone.