Unlocking the hidden world of Hector’s dolphins

The underwater lives of the endangered Hector’s dolphin have been revealed for the first time by marine scientists working to ensure we don’t lose the Hector’s, and even rarer Māui dolphins forever.

Scientists observing from boats knew little of the underwater behaviour of the world’s smallest marine dolphin, until now.

Innovative tracking devices known as DTAGs have enabled the researchers to reconstruct the underwater life of the Hector’s dolphin. And their just released scientific paper has revealed a hidden world – including an array of acrobatics.

Dives to 120m deep, journeys 15km offshore, barrel rolls midwater to catch schooling fish, upside-down feeding near the seafloor and moments of silence – no echolocation, leaving them more vulnerable to fishing nets were among the behaviours discovered through the tracking devices.

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.

In a trial in the Clifford and Cloudy Bay Marine Mammal Sanctuary at the top of the South Island, the 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.

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

“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 minimise the risks to the dolphins and to know how they behave in other locations.”

The fine-scale analysis, supported by Live Ocean, the Bethell Family Foundation, the Department of Conservation, the Ministry for Primary Industries and the University of Auckland – Waipapa Taumata Rau, has already challenged assumptions underpinning current protection zones. Static sanctuaries may not align with where and how these dolphins are actually living.

The preliminary work, done in Clifford and Cloudy Bay is only the beginning. To understand whether these behaviours are consistent across populations, further DTAG studies are needed in other high-risk areas such as Timaru and Kaikōura.