Dolphins in Australia Are Beaching Themselves As Part of an Unusual and 'Risky' Feeding Behavior

Researchers have documented a risky feeding behavior in Australian humpback dolphins, known as "strand feeding," using drones equipped with cameras.

This predatory strategy involves dolphins swimming towards the shore, emerging out of the water, and beaching themselves on beaches or mud banks in order to feed on small fish, which are sometimes washed onto the shore by the wave that is generated.

"Strand feeding occurs where dolphins patrol the mud banks in search of a prey; once the prey has been localised a dolphin swims at high speed toward the shore, catches the fish in its mouth and remains stranded for a short time before sliding gently back into the water," Daniele Cagnazzi, a researcher from Southern Cross University in Australia, said in a statement.

"This type of feeding is very risky, as dolphins run the risk of remaining stranded, however, since this behaviour is routinely repeated it must provide an important proportion of their daily feeding needs—dolphins must consume 4-6per cent of their own body weight in fish each day," Cagnazzi said.

Strand feeding was first observed in bottlenose dolphins living in the waters of marshes in South Carolina and Georgia. In the decades since, the behavior has only been documented in a handful of locations around the world—primarily in bottlenose dolphins, but also in killer whales, according to a 2015 study published in the journal Latin American Journal of Aquatic Mammals.

When it comes to Australian humpback dolphins—a dolphin species that was only scientifically described for the first time in 2014—the behavior is only consistently seen in one location.

"This behavior is very difficult to see in the wild because you need to be at the right time and in the right place, and hope that dolphins will show off," Cagnazzi told Newsweek. "This feeding technique has been observed with slight variations in other species and regions around the world. The most famous being in Charleston, South Carolina, around which a dolphin-watching industry developed.

"The Fitzroy River is the only location where this behavior has been observed consistently, providing a great opportunity to document it. I have observed this behaviour multiple times since 2009, once I understood the conditions needed by dolphins to strand feed. However, the first video of partial strand feeding was captured only in 2014. Last year for the first time we have been able to document extensively this behaviour from the air using drones," he said.

For his recent observations, using drones Cagnazzi filmed a pod of dolphins living in the Fitzroy River in the eastern Australian state of Queensland. The Australian humpback dolphins in this river are the only members of their species in the country that are known to reliably engage in this behavior. Cagnazzi has been studying this group for more than a decade.

"This strand feeding behaviour is conducted primarily by a very well-known family group of humpback dolphins who we've identified as long-term residents in the Fitzroy River," he said. "The number of dolphins involved in a single episode varies from one to two while the rest of the group is busy in other activities and strand feeding can be full body or partial."

In 2014—soon after Australian humpback dolphins were identified as a distinct species—Cagnazzi described similar observations of strand feeding, noting how the technique could help the animals to catch fish.

"The humpback dolphins were observed swimming a few metres away from and parallel to the shoreline," he told Business Insider Australia. "This behavior 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," he said. "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."

Australian humpback dolphins
Stock photo: An Australian humpback dolphin under water near the east coast of Australia. iStock

According to Cagnazzi, this feeding behavior occurs during low tide when mud banks are exposed. As a result, anything that affects the river habitat—such as flooding or sedimentation—could have an impact on the ability of these dolphins to feed.

"Every year before returning to the field, we worry that we will not witness this incredible behavior again. In the last decade, the habitat of the Fitzroy River humpback dolphins has been subject to an unprecedented increase in frequency of large flooding events. Increases in river bank erosion, sedimentation and turbidity, and poor water quality can all be expected to result in the loss of habitat for Australian humpback dolphins, including habitat which is suitable for strand feeding," Cagnazzi said.

"This behavior 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," he said.

The International Union for Conservation of Nature "Red List" designates Australian humpback dolphins as "Vulnerable," however, there is no global population estimate and Cagnazzi says that we know relatively little about some aspects of their behavior.

"From here we are aiming to use the analysis of photographic and genetic data to determine if this strand feeding behaviour is culturally transmitted from the mothers to calves," Cagnazzi said.

Researchers have observed dolphins employing a wide variety of techniques to catch prey, including following boats to feed on discarded fish; wearing marine sponges on their snouts in order to protect these sensitive body parts while foraging for food on the seafloor; and smacking their tails over shallow water to shock and stun prey, according to marine environmental charity Sea Watch Foundation.

This article was updated to include additional comments from Daniele Cagnazzi.