In the waters of a marine-protected zone near the Australian coast, certain bottlenose dolphins are frequently spotted with sponges affixed to their noses. Unlike orcas adorning themselves with salmon or chimps inserting grass in peculiar places, the act of “sponging” serves a practical purpose rather than a fashion statement or cultural norm.
This unique foraging technique, passed down through generations, involves dolphins using sponges to stir up fish from the seabed effectively. According to marine biologist Ellen Jacobs from the University of Aarhus in Denmark, the origin of sponging likely began with a single dolphin’s creative discovery of using a sponge to scare up fish, which was then transmitted to its offspring and continued over time.
A recent study led by Jacobs, published in the Royal Society Open Science journal, delves into the advantages and drawbacks of sponging, investigating why this technique is limited to a specific genetically related dolphin population in the marine-protected environment of Shark Bay.
The sponging process entails dolphins placing a sea sponge on their noses to disturb fish hiding among rocks and shells on the seabed. However, only a small fraction, about five percent, of the dolphin population in Shark Bay engages in sponging, with roughly 30 dolphins observed practicing this behavior. Notably, sponging is a skill passed down matrilineally, with calves learning it from their mothers.
Researchers are intrigued by the limited spread of sponging among dolphins, which seems to propagate vertically from adults to juveniles but not horizontally between peers or groups. Despite its benefits, sponging poses challenges. It is time-consuming and requires years to master due to the distortion it causes in dolphins’ echolocation, essential for navigation.
While sponging demands patience and skill, those who excel at it enjoy year-round access to non-migratory fish, which are the primary target of this specialized hunting technique. Additionally, the fish found in the sediment may offer higher nutritional value than other fish species.
Apart from sponging, other tool-use behaviors have been observed among bottlenose dolphins in Shark Bay, such as using sea shells to catch and eat fish, referred to as “shelling” or “conching.” These unique behaviors thrive in the pristine ecosystem of Shark Bay, free from pollution and overfishing stresses that affect many dolphins worldwide.
By studying these dolphins in their natural habitat, researchers aim to gain insights into how dolphins thrive without human-induced impacts, providing valuable knowledge on the natural behaviors of these intelligent marine mammals.
