Inside Nature's Giants

Who: carnivore

What: eats small fish (herring, capelin, sand lance) & crustaceans (krill) & squid

Where & When: usually near surface, plankton layer, usually in daytime (easier to see prey from below when they are silhouetted against light at water's surface)

Interesting fact: Whales derive all their drinking water from ingested food, not from seawater.

How?

Counter-shading: Asymmetrical skin coloration of the fin whale’s head may allow side feeding due to counter-shading (right side jaw and baleen are white, while left side is dark grey to black). If the right side is down while feeding, then prey above whale look down and do not see dark left side of the whale rising, while prey below whale look up and do not see right white side of the whale silhouetted against lighter sky.

Jaw protrusion: The mouth opens with an unusual jaw joint that allows the lower jaw to partially dislocate from the skull and be thrown forward of the rostrum (forward tip or 'muzzle'). This increases the gape of the already very large jaws. Like a snake, the whale can engulf a large volume – larger than its head!

Engulf: The extremely large gape is paired with an expandable throat pouch in the floor of the mouth. This helps whale engulf a large volume of water containing prey (like the stretchy throat of the pelican). Opening the jaw while swimming forward means that the pressure of the water will help expand the throat pleats, which open like a parachute.

Close mouth: It is hard to close the mouth by moving the lower jaw, which is weighed down with all that water. The whale aids this action by swimming forward, pushing its head over the lower jaw and expanded throat (floor of the mouth). This helps to retract the protruded jaw joint, and places some weight on the mouth region, thereby forcing the head down. That action, in turn, puts water pressure on the outside of the throat pleats, which helps to force them to contract. Muscle in the throat also contracts the throat into pleats (like a collapsing accordion), forcing the water to exit the mouth.

Strain: The prey must be separated from the water. The collapsing throat pleats force the water to exit the mouth, with is mostly closed. The small gap is lined with baleen, which resembles a moustache. The water is forced through the gaps between each plate of baleen (there are no teeth). The baleen plates (which are comprised of keratin – a substance much like fingernails) have a fibrous edge facing the tongue. These fibres overlap adjacent baleen plates, forming a woven mesh. As water passes through the mesh, prey is caught in the weave and is prevented from leaving. Coarse baleen fibres are found in species that eat large prey (e.g., fin whales), while fine baleen fibres are found in species that eat very tiny prey (e.g., right whales).

Swallow: Whales use the tongue to wipe food off of the baleen fibres (like licking food off a moustache!). The food then passes as a slurry of small prey items through a small opening into oesophagus and then to stomach. (Although Jonah could fit into a whale's mouth, he certainly would not have been swallowed through that tiny opening into the stomach!)

Stomach: This organ resembles the condition in artiodactyls (cud chewing mammals with horns or antlers, like deer, cattle, antelope, sheep). This is unusual, as a 4 chambered stomach is a trait of herbivorous animals. Thus, the presence of such a stomach indicates the whales evolved from a terrestrial herbivorous ancestor – probably also the ancestor to modern artiodactyls.

Intestines: Whale have a relatively simple tube. It is difficult to determine where the small intestines end and the large intestines (colon) begin. However, there is a small cecum (a sac, much like our appendix) at the junction. Before the cecum, the intestines are highly folded, and after the cecum the intestines re fairly straight, particularly he last part that runs between the large bundles of muscle under the vertebral column that depress the tail during swimming.

Faeces: whale faeces are relatively liquid and appear like diarrhoea. It would be difficult for a whale to do a valsalva manoeuvre to push out solid faeces, so loose stool is the norm.