Sowerby

Researchers surprised by unusually fast beaked whales deep-sea hunting strategy

Beaked whale from Sowerby. Credit: NOAA Fisheries

An international team of biologists has successfully used biologgers to gain insight into the lifestyle and hunting behavior of Sowerby’s little-known beaked whale. The team’s first results show that these whales (which resemble dolphins) have surprisingly different, much faster-paced lifestyles than related species. The research was led by Fleur Visser of the University of Amsterdam (UvA) and the Royal Netherlands Institute for Sea Research (NIOZ). The results were published on May 12, 2022 in the Journal of Experimental Biology

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

With 16 species, the so-called Mesoplodont whales make up 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 past 30 years. Most species are physically very similar and all are believed to be specialized deep-sea predators. In addition, they often occur in the same areas and forage at similar depths. This raises the question of how they can avoid mutual competition for the same prey.

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

Bilogging

For a few species of beaked whales, biolog tags, which are attached to their backs with suction cups, have been shown to typically lead low-energy lifestyles: They can make extremely deep dives through slow, energy-saving swimming styles and hunting strategies. But Sowerby’s beaked whales had never been spotted before. However, after years of effort, the research team was able to deploy biolog tags on two Sowerby’s beaked whales. The tags recorded detailed information about the diving, movement and echolocation strategies of these extremely shy animals, providing the first opportunity to investigate their foraging behaviour. This allowed for a direct comparison of their hunting strategies with those of their closest relatives, the slow-moving Blainville’s beaked whale.

Sowerby's beaked whale (Mesoplodon bidens)

Sowerby’s beaked whale (Mesoplodon bidens) pops up in the waters off Terceira Island, Azores. The species’ distinctive long bill sticks out of the water as it emerges. Credit: Kelp Marine Research

Surprise

Much to the researchers’ surprise, Sowerby’s beaked whales differ greatly from other Mesoplodon species in their swimming and hunting strategies. While aiming for a similar foraging depth (800-1,300 meters/2,600-4,300 feet), they consistently swim faster, make shorter deep dives and echolocate faster, with higher frequency clicks. This first sighting 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 developed a wider range of specialized strategies 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 man-made sounds, which appear to be highly behavioral in other species.

Reference: “Sowerby’s beaked whale biosonar and locomotion strategy indicate deep-sea foraging niche differentiation in mesoplodont whales” by Fleur Visser, Machiel G. Oudejans, Onno A. Keller, Peter T. Madsen, and Mark Johnson, May 12, 2022, Journal of Experimental Biology
DOI: 10.1242/jeb.243728


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