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Australian researchers finally able to study voluntary beaching in humpback dolphins

Humpback dolphins, a species only scientifically described in 2014, shows a startling behaviour in the Fitzroy River in eastern Australia. In a predatory strategy called Strand feeding, they patrol the mud banks in search of prey. Once localized, they swim towards the shore at high speed and beach themselves on the mud banks to feed on the fish carried there by the waves. Thanks to the soft mud, they usually slide back into the water within under a minute. Nevertheless, the behaviour is extremely risky for such a small reward, as the 250 kg animals are likely to remain stranded on the beach if the circumstances are not right.

Such behaviour has only been observed in a handful of species and locations around the world. It has first been observed in bottlenose dolphins in South Carolina and Georgia, later followed by further bottlenose observations in other places, as well as killer whales. Observations are extremely difficult as you need to be at the right place at the right time. The Fitzroy population of humpback whales is the only one that has been showing the behaviour consistently.


Australian researchers around Dr Daniele Cagnazzi from the Southern Cross University have for the first time been able to document and study the population with drones. They conclude that “since this behaviour is routinely repeated it must provide an important proportion of their daily feeding needs – dolphins must consume 4-6 per cent of their body weight in fish each day.”

Because the strand feeding is primarily shown by females with juveniles, the researchers are now “aiming to use the analysis of photographic and genetic data to determine if this strand feeding behaviour is culturally transmitted from the mothers to the calves”. The well-studied population with their consistent presentation presents an optimal study object to understand the behaviour better.

A population of humpback dolphins in the Fitzroy River is the only population that shows strand beaching consistently (Photo: Southern Cross University)

On a concerning note, the behaviour also “highlights the strong connection of this species with the coastal habitat, and the importance of a highly diverse environment for the survival of this population and species”. The feeding behaviour is reliant on low tides that expose mud banks and therefore highly affected by anything that affects the river habitat. Alas, flooding events have increased in the Fitzroy River during the last decade, resulting in increased erosion of the river banks as well as sedimentation and pollution. Cagnazzi admits that they worry “every year before returning to the field […] that we will not witness the incredible behaviour again.” The Australian humpback dolphin is listed as Vulnerable in the IUCN Red List but there is no global population estimate. Cagnazzi and colleagues will keep monitoring the population and keep working on understanding their behaviour better.




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