Rare moment captured as elusive dolphin species beaches itself to feed on fish

A rare and elusive Australian dolphin species that sometimes beaches itself to feed has been captured on camera for the first time by Southern Cross University scientists.

The unusual behaviour was displayed by a pod of near-threatened Australian humpback dolphins (Sousa sahulensis) in the Fitzroy River estuary of central Queensland in July. Watch the video

It is the second time in three years that the Capricorn Cetaceans Research Team, led by Dr Daniele Cagnazzi, a postdoctoral research fellow with the University’s Marine Ecology Research Centre, has observed the stranding behaviour in Australian humpback dolphins during boat-based surveys.

Dr Cagnazzi said initially it was large splashes in the distance that attracted the team’s attention.

“We soon realised we were witnessing an incredible event. The humpback dolphins were observed swimming a few metres away from and parallel to the shoreline. This behaviour probably allows dolphins to concentrate fish against the mud bank before charging at them at high speed. On some occasions the fish were washed onto the shoreline by the wave of water associated with the dolphin's beaching, resulting in a full body exposed beaching. On other occasions the stranding was only partial with more than half of their body exposed.

“In these shallow waters the agility of the dolphin’s neck region enabled them to reach for the stranded fish before sliding back into the deeper water, thanks to the soft mud substrate.”

The fish being ‘rounded up’ were sea mullet (Mugil cephalus).

On October 1, 2011 the Capricorn Cetaceans Research Team, again working in the Fitzroy River estuary, spotted one animal which appeared to be stranded and dead on a mud bank.

“However, it was soon apparent that the animal was alive when after a few seconds it slid back into the water,” said Dr Cagnazzi.

The Fitzroy River, one of the largest rivers in Australia, is a macrotidal, tide-dominated estuary located in the dry tropics of central Queensland. The area features a network of narrow deep creeks and channels with steep muddy edges, providing the perfect habitat for the display of this behaviour.

Prior to this, the only other written report of beach hunting behaviour in Australian humpback dolphins was in 2007 near Cape Van Diemen in the Northern Territory. In this event humpback dolphins were observed pushing fish onto exposed sand banks at low tide and surging partially onto the banks to catch them. However no photographic or video evidence was collected.

Dr Cagnazzi said dolphins around the world used a number of foraging strategies.

“One of the most spectacular and rare behaviours is the ‘strand-feeding’ or ‘intentional beach hunting’ which involves one or more dolphins surging partially or fully out of the water and onto the beach to catch a single fish.

“The variety and complexity of these techniques, as well as the manner in which they are passed down from adults to their young, presents evidence for social learning and may qualify as a type of animal ‘culture’.”

Until now, the rare ‘beach hunting’ behaviour has been documented in only two species: Orca (Orcinus orca) in Argentina; and bottlenose dolphins (Tursiops sp.) in the water estuaries of Georgia and South Carolina in the US, Sado Estuary in Portugal, and Shark Bay and Peron Peninsula in Western Australia. A similar behaviour was also observed on one occasion in 1994 with Indian humpback dolphins (Sousa plumbea) near the Bazaruto Archipelago in Mozambique.

Professor Peter Harrison, director of the University’s Marine Ecology Research Centre, said the observation by the Capricorn Cetaceans Research Team was significant.

“These new observations of complex feeding behaviours in inshore dolphins highlights the lack of knowledge we have about key aspects of the ecology and biology of these important dolphins and most other cetacean species in Australian waters.”

The Capricorn Cetaceans Research Team will keep collecting information to better understand the factors promoting this behaviour.

The Capricorn Cetaceans Research Project is supported by Fitzroy Basin Association Inc. through funding from the Australian Government and Southern Cross University.

Photo: Australian humpback dolphin (Sousa sahulensis) strand-feeding in the Fitzroy River estuary of central Queensland in July 2014 (Credit: Fiona Wardle from Capricorn Cetaceans Project).