Cuvier's Beaked Whale

Morphlogy

Superficially speaking, Cuvier’s┬ábeaked whale is similar to other members of the beaked whale family. They grow up to 7 meters in length and 3000kg in weight, with little sexual dimorphism (Jefferson et al.,1993). Males of the species have two cone-shaped teeth in the tip of their bottom jaw that are possibly used when fighting. They have a small triangular dorsal fin and narrow flippers that can be tucked into grooves in its body wall to create a very streamline form that minimises drag when diving (Taylor et al., 2008). The dolphin-like beak, characteristic of beaked whales, is present, but is not as prominent in this species (Jefferson et al.,1993). They range from dark grey to reddish brown in colour caused by algae build up on the skin surface, with a paler underside. Due to competition for mates, the skin of males are often covered in pale parallel linear scratches and scars caused by the teeth of other males (Jefferson et al.,1993). Beaked whales, unlike other toothed whales, have reduced teeth and are suction feeders, which is facilitated by a pair of grooves running along the throat and allows the mouth to expand, sucking in water, and prey, rapidly (Rommel et al., 2005).

The scull of Ziphius, extracted from Marine mammals of the world. Jefferson et al. 1993.

The scull of Ziphius, extracted from Marine mammals of the world. Jefferson et al. 1993.

Beaked whales have several physical adaptations that make their extreme vertical foraging expeditions possible. They are able to slow their heart rate to control their blood flow in such a way that ensures the vital organs get enough oxygen (Rommel et al., 2005). Doubling the pressure means that the volume of gasses present is halved, meaning way before the maximum dive depth has been reached, the lungs collapse and prevent any gas exchange, meaning that nitrogen in the lungs can’t be absorbed (Rommel et al., 2005). This prevents nitrogen build up in tissues that could cause nitrogen bubbles forming when returning to the surface, and result in decompression sickness.

 

Cuvier’s beaked whales have huge levels of myoglobin, allowing them to store very large levels of oxygen in their muscle tissues and increases the time they are able to hold their breath (Rommel et al., 2005). The length of time large animals are able to forage at depth is dependent on their aerobic dive limit, or how long they are able to dive aerobically for without the levels of lactic acid in the whales tissues becoming too high (Tyack et al., 2006). The actual maximum aerobic dive limit, based on metabolic rates, of Ziphius is not known. However, assuming that the oxygen carrying capacity of Ziphius is similar to that of the Weddell seal, which has one of the highest known capacities of any diving animal, and that the metabolic rate of both species increases similarly with increase of muscular tissues, an estimate can be made. Calculated in this manner, this puts the maximum estimated aerobic diver time of Ziphius at 33 minutes (Tyack et al., 2006). This is over 100 minutes less than the longest recorded dive and barely covers the time is takes for them to reach the depths at which they feed. This means that Ziphius must in some part rely on anaerobic respiration when at depth, and means a long time is needed for recovery after each dive (Tyack et al., 2006). This diving method represents a physiological trade off; in order to reach the depths at which they feed they must sacrifice dive efficiency.

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