Indo-Pacific bottlenose dolphins around Shark Bay, Australia, perform a unique behavior called “sponging”, which is where certain animals place sponges over their snouts during foraging activities. Not all of the dolphins in this area display the behavior, and it was discovered that sponging was in fact culturally transmitted. Although it seemed plausible that sponging could be classified as tool use, it remained a mystery what the precise purpose of this behavior was; scientists postulated that it could serve to protect their beaks against abrasion from sharp objects whilst foraging for food.
A new study aimed to shed light on why these animals might be using these sponges; in particular, whether sponging allowed the animals to access certain novel resources that non-spongers could not. They found evidence that the animals used sponges as tools to access food, meaning that they could exploit an otherwise unused niche. The results have been published in the journal Proceedings of the Royal Society B.
The scientists took biopsy samples from the blubber of 11 spongers and 27 non-spongers in order to analyze and compare the tissues. They were interested in fatty acid (FA) content because this reflects what prey they are consuming. The team found that the FA profiles were completely different between spongers and non-spongers. Furthermore, the difference was significant between spongers and non-spongers that were foraging in the same habitat, whereas non-spongers foraging in different habitats had indistinguishable profiles.
Taken together these results demonstrate that this apparent tool use behavior enables the dolphins to exploit foraging niches that non-spongers cannot. “This has been demonstrated in only a few species so far, and has been implicated as a significant driver for human evolution,” said Michael Krützen, lead author of the study.
It is possible that the sponges allow the dolphins to target bottom-dwelling fish that do not possess swim bladders, since the complex sea floor makes detection via echolocation difficult. As it stands it remains unclear what this novel prey is, but future studies may look into this.