In a designated marine sanctuary near the Australian coast, a group of bottleneck dolphins has been observed swimming with sponges affixed to their noses. This behavior, known as “sponging,” is not a mere fashion statement or cultural trend like orcas adorning themselves with salmon or chimpanzees inserting grass into their ears and anuses.
Instead, sponging is a sophisticated foraging technique that has been passed down through generations within this dolphin community. Marine biologist Ellen Jacobs from Denmark’s University of Aarhus explained that sponging likely originated from a single innovative dolphin that discovered the effectiveness of using a sponge to stir up fish from the seafloor. Subsequently, this technique was adopted by offspring, leading to its perpetuation.
A recent study published in the Royal Society Open Science delves into the advantages and limitations of sponging within this specific population of genetically linked dolphins in Shark Bay. Only a small percentage of the dolphin population, approximately 30 individuals, engage in sponging, predominantly passed along matrilineally from mothers to calves.
Sponging involves a dolphin placing a sea sponge on its nose to disturb fish hiding among rocks and shells on the seabed. Despite being initially reported in 1984, the behavior remains exclusive to a select few dolphins in Shark Bay. Researchers have questioned why sponging has not spread widely among dolphins and discovered that it primarily transfers vertically from adults to juveniles, rather than laterally among peers.
The study reveals that sponging presents challenges, including being time-consuming and requiring years of practice to master due to the distortion of echolocation caused by the sponges. Dolphins using sponges have to adapt to this distortion, akin to navigating with the wrong prescription glasses, as explained by Jacobs and corroborated by marine biologist Mauricio Cantor.
Nevertheless, dolphins proficient in sponging benefit from a consistent food supply, as the fish they target are non-migratory and less contested due to the limited number of sponging dolphins. Research also suggests that fish found in sediment may offer higher nutritional value compared to other sources.
Apart from sponging, other instances of tool use, such as using shells to scoop fish, have been documented among bottleneck dolphins in Shark Bay. Jacobs highlights the pristine nature of the environment in Shark Bay, free from pollution and overfishing, which allows the dolphins to exhibit their natural behaviors without human-induced stressors.
This unique ecosystem offers valuable insights into understanding the natural behavior of dolphins and underscores the importance of preserving such environments for marine life.