World's smallest marine dolphins can perform underwater barrel rolls

September 19, 2025

World's smallest marine dolphins can perform underwater barrel rolls

by Paul Panckhurst,

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World's smallest marine dolphins perform underwater barrel rolls — Hector's dolphin depth-dependent postural modes while foraging in benthic dives. Credit: *Conservation Letters* (2025). DOI: 10.1111/conl.13144

Scientists observing from boats knew little of the underwater behavior of the world's smallest marine dolphin, the Hector's dolphin.

Now, a paper has revealed a hidden world鈥攊ncluding an array of acrobatics. The research is in the journal Conservation Letters.

Barrel rolls, dives up to 120m deep, and upside-down feeding near the sea floor were behaviors discovered through tracking devices.

"There are some seriously impressive dives," says University of Auckland scientist Dr. Ilias Foskolos, lead author of the study. "Swimming down to 120 meters, that's quite something for a 1.4 meter long animal鈥攊t wasn't what we expected."

Scientists have created animations of one dolphin's dives, accompanied by the sounds of the mammal's echolocation clicks, which turn into a buzz like a power tool when targeting prey.

University of Auckland scientists have used tracking data to recreate dives by a Hector's dolphin. Animation shows a dive in real time using tracking information. Triangle = surfacing (you can hear the splash as it breaks the surface and the breath) Circle = moves as the dolphin dives down Blue line = dorsal side up Yellow line = upside down as the dolphin barrel rolls (on the shallow dive) or swims just above the seabed (on the deep dive) Red starbursts = when the dolphin chases a fish, preceded by a 'buzz', a fast series of clicks that they use when targeting their prey Clicks = the slower click, click, click is the dolphin's echolocation sound Continuous gentle 'woosh' = the sound of water running over the tag as the dolphin dives or surfaces (like the sound of wind passing if you were riding a bike) Thin grey line on seabed = indicates the total path of the dolphin track. Credit: University of Auckland

In a trial in the Clifford and Cloudy Bay Marine Mammal Sanctuary at the top of the South Island, sound and movement recording devices called DTAGs, developed by New Zealand-based Professor Mark Johnson, were attached to 11 Hector's dolphins using suction cups.

The dolphins switched tactics depending on where they were feeding, the recordings showed.

Near the seabed, they cruised slowly, flipping upside down to nab flatfish and cod. In midwater, they ramped up the energy, executing barrel rolls to catch small, schooling fishes.

The furthest offshore a dolphin swam was 15km.

University of Auckland Professor Rochelle Constantine says the study has demonstrated the value of the tracking devices.

University of Auckland scientists have used tracking data to recreate dives by a Hector's dolphin. Animation shows a deep nighttime dive in real time using tracking information. Credit: University of Auckland

"Despite this being a preliminary study, we can clearly see the value of the DTAG for understanding risks such as interactions with fishing gear or vessels," says Constantine. "It's important to continue this work to better understand how to minimize the risks to the dolphins and to know how they behave in other locations."

About 15,000 Hector's dolphins live in coastal waters around the South Island鈥攖heir only habitat.

Marine Mammal Sanctuaries seek to manage the overlap between fishing and dolphin habitats, alongside protections through the government's Threat Management Plan.

More information: Ilias Foskolos et al, Subsurface Behaviors of Hector's Dolphins Could Increase Their Risk of Bycatch, Conservation Letters (2025).

Journal information: Conservation Letters

Provided by University of Auckland

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