Researchers surprised by the deep-sea hunting strategy of an exceptionally fast beaked whale

Sowerby’s beaked whale. Credit: NOAA Fisheries

Beaked whales include a number of marine mammal species that can perform record dives. They regularly visit depths of up to several kilometers on hour-long hunting trips in search of squid and deep-sea fish. Due to their elusive nature and limited surface presence, little is known about their behavior.

With 16 species, the so-called Mesoplodon whales form the largest genus of cetaceans. The genus includes some of the least known marine mammals, so much so that three new species of these rhinoceros-sized whales have been discovered in the last 30 years alone. Most species are physically very similar and are all assumed to be specialized deep-sea predators. Additionally, they are often found in the same areas and feed at similar depths. This raises the question of how they can avoid competition with each other for the same prey.

Sowerby’s beaked whales (Mesoplodon bidens) surface in the waters off Terceira Island, Azores. Credit: MG Oudejans @Kelp Marine Research

Biologging

For a few species of beaked whales, biologging tags, attached to their backs with suction cups, revealed that they generally have a low-energy lifestyle: they are able to perform extremely deep dives thanks to to slow, energy-efficient swimming styles and hunting strategies. . But Sowerby’s beaked whales had never been tagged before. However, after years of effort, the research team was able to deploy biologging tags on two Sowerby’s beaked whales. The tags recorded detailed information about the dive, movement and echolocation strategies of these extremely shy animals, providing the first opportunity to study their foraging behavior. This made it possible to directly compare their hunting strategies with those of their close relatives, the slow-moving Blainville beaked whale.

Sowerby’s beaked whale (Mesoplodon bidens) surfacing in the waters off Terceira Island, Azores. The species’ characteristic long beak protrudes from the water when surfacing. Credit: Kelp Marine Research

Surprise

To the researchers’ surprise, Sowerby’s beaked whales differ greatly from other mesoplodon species in their swimming and hunting strategies. While targeting a similar foraging depth (800 to 1,300 meters / 2,600 to 4,300 feet), they consistently swim faster, perform shorter deep dives, and echolocate at a faster rate, with more frequent clicks . This first record of a ‘fast’ beaked whale suggests that Mesoplodon whales exploit a greater diversity of deep-sea niches than previously suspected. The deep sea is a rich and diverse hunting ground for marine mammal predators, who have clearly evolved an array of specialized strategies to be able to exploit it than previously known. The marked departure of Sowerby’s beaked whales from the generally slower behavior of other beaked whales also has potential implications for their response to artificial sounds, which appear to be strongly behaviorally motivated in other species.