11.10.2018 – Exception to the rule

The toothed whale family (Odontoceti) members show a variety of hydrodynamic body shapes which determine how they surface to breathe. This is partially why swim behavior and water spouts are key identification features of different species for our crew at sea. Apart from the frequently encountered Bottlenose dolphins (Tursiops truncatus) and serenely calm Short-finned pilot whales (Globicephala macrorhynchus), we also managed a sighting at close range with Blainville’s beaked whales (Mesoplodon densirostris).

The common name for the Ziphiidae, “Beaked whales”, is derived from the swimming behaviour of the animals who surface beak-first before exposing their blowhole. A guest asked a very interesting question after the sighting; do some cetacean species also use their mouths to breathe?

Generally speaking, the answer is no. Cetaceans use their blowhole for respiration, which occurs as a single hole in toothed whales and as a divided opening in baleen whales (Mysteceti). The blowhole is infact the animals nose and breathing occurs when it is exposed at the surface before it is once again tightly sealed by strong muscles as the animal dives. Breathing only through their blowhole and not through their mouths allows cetaceans to separate respiration and feeding efficiently, preventing water from entering their lungs as they ingest prey.  The characteristic water-spout we see when the animals exhale at the surface does not come from the animals body; it is the water sitting at the top of their heads that is projected to the surface as they exhale. Another evolutionary adaption to breathing through the blowhole is the “goosebeak” or laryngeal plug, a bizarre plug that essentially reaches into the nasal cavity near the blowhole. This plug completely separates the respiratory and digestive tracts of the animal. It is also a wide belief amongst scientists that, although dolphins have a degree of muscular control over this plug, they would never attempt to move it to breathe through their mouths and risk drowning.

There is, however, an exception to the rule. In New Zealand a Hector’s dolphin (Cephalorhynchus hectori)is the first documented mouth-breathing dolphin and is making scientists think twice about their assumptions. The animal, easily recognisable through a “tatoo” lesion surrounding its melon, surfaces at a steep angle sucking in air through its mouth, keeping its blowhole tightly sealed in the process.  Researchers believe that something may be blocking its nasal passages leading to it actively moving the laryngeal plug to suck in air through its mouth.

I truly appreciate such questions from our guests because they give me the urge to go find some answers after the tour. Regardless of the question, what I always dicover is that, no matter how much research on cetaceans has advanced in the past decades, these animals never fail to surprise us.

By Paula Thake

Sightings of the day

Stenella

10:00 Blainville’s beaked whales, Bottlenose dolphins, Short-finned pilot whales