A fascinating foraging behaviour observed among some dolphins in Australia involves a particular technique for dislodging fish from the seafloor. This practice, known as “sponging”, protects their beaks from getting damaged by sharp rocks as they carefully sift through rubble in sandy channels at the ocean’s bottom. This disturbance effectively stirs up prey, like barred sandperch, making them easier to catch. Recent research in the journal Royal Society Open Science shows that this behaviour is more complex than it first appears.
Hunting with a sponge on their beaks significantly affects bottlenose dolphins’ refined sense of echolocation. Co-author Ellen Rose Jacobs, a marine biologist from the University of Aarhus, Denmark, described the effect as “muffling,” similar to wearing a mask. She explained that while the sensory input may seem slightly distorted, the dolphins can learn to adjust for this change. To confirm that the sponging dolphins in Shark Bay, Australia, were still using echolocation clicks for guidance, Jacobs used an underwater microphone. She then created a model to measure how much sound wave distortion the sponges caused.
Despite the challenges, scientists say that for wild dolphins trained in foraging with nose sponges, this method is an efficient way to catch fish. These sponges, which range in size from a softball to a cantaloupe, provide essential protection. Mauricio Cantor, a marine biologist at Oregon State University who wasn’t part of the study, compared sponge hunting to “hunting when you’re blindfolded.” He stressed that it requires exceptional skill and extensive training to do it successfully.
The difficulty of this foraging technique may explain its rarity. Researchers studying the dolphin population in Shark Bay found that only about 5% of the dolphins, or around 30 individuals, engage in sponging. Marine ecologist Boris Worm from Dalhousie University in Canada, who also wasn’t involved in the study, noted that “It takes them many years to learn this special hunting skill; not everybody sticks with it.” Dolphin calves usually stay with their mothers for about three to four years, during which they watch and learn important life skills.
The delicate art of sponge hunting is passed down exclusively from mother to offspring, according to co-author and Georgetown marine biologist Janet Mann. This maternal lineage shows that this behaviour is learnt and passed down within the dolphin community. The study, supported by The Associated Press Health and Science Department along with contributions from the Howard Hughes Medical Institute’s Science and Educational Media Group and the Robert Wood Johnson Foundation, enhances our understanding of the intelligence and resilience of these animals in adjusting to their environment.
