In Shark Bay, Western Australia, a subset of the bottlenose dolphin population displays remarkable ingenuity. When foraging, they cover their snouts with a sea sponge in order to search the seabed. The use of such a tool is rare amongst cetaceans and this behaviour, transmitted from mother to offspring, gives them access to a unique diet.

Prey unearthed

Deep in the channels of Shark Bay, a small portion of the bottlenose dolphin population exhibits never-before-documented behaviour, which was described in an article published in 2008. These dolphins use sea sponges to stir up the sandy seabed in search of prey. To do so, the cetaceans completely cover their snouts and jaws with a cone-shaped sponge, which protects them from ray bites, scratches and dangerous organisms. This technique forces the fish to come out of their hiding place and travel a few metres before they bed down in the sand again, which allows the dolphins to make a mental note of their location. This activity is much more popular amongst females, which account for the majority of “spongers.” However, only a little over one-tenth of the females in this population have adopted this specialized technique.
One question inevitably arises when witnessing such behaviour, which is performed only by a subgroup of individuals. Does sponge use offer any advantages? If it does, the answer is not obvious, as female spongers spend more time alone or together with their young, associate less with their peers, carry out longer dives with steeper descents and make greater use of the deep channels. In short, these specialized dolphins devote a greater portion of their time foraging for food. However, despite these apparent trade-offs, sponge users enjoy reproductive success that is comparable to that of their non-sponging peers.

Mom taught me!

The existence of distinct feeding techniques within the same population suggests the influence of various factors such as genetic predispositions, different ecological conditions or even social learning. In the bottlenose dolphin, mastering sponge use is mainly a social learning process the transmission of which is vertical or matrilineal, explain the researchers of a study released in 2019. This skill is therefore passed on from mothers to their offspring. In fact, females adopt the practice in larger numbers than their male counterparts, only half of which make use of this hunting technique. To date, no case has ever been documented of sponging in which the individual did not first learn the practice from its mother.

A number of explanations concerning this behavioural difference between males and females have been put forward. Males, which maintain extensive territories, dedicate a great deal of their time to socializing, alliance forming playing a key role in their reproduction. Indeed, males will work together in order to force ovulating females to mate. This reproductive strategy is difficult to reconcile with sponging, a difficult-to-learn, time-intensive technique that can only be practised when alone.

As for females, they tend to study their mother’s behaviour more carefully, be it for foraging techniques or habitat use, in addition to striving to optimize their food intake with more elaborate hunting techniques. Scientists have also suggested that encouraging the transmission of this knowledge to female offspring could be advantageous for mothers since they, unlike males, will be able to transmit this knowledge to the next generation.

An environment to discover

Although this subset of dolphins uses a unique foraging technique and feeds primarily in deep channels, the impact of these elements on the animals’ diet has long remained a mystery. Does the sponge technique provide access to otherwise hard-to-reach prey? The answer is yes, according to a study published in 2014. Analyses of the fatty acids of bottlenose dolphins frequenting the deep channels of the western gulf of Shark Bay revealed that the diet of spongers differs from that of the rest of the population. In contrast, the diets of dolphins that do not use sponges but that feed in different habitats are similar. However, it is not possible to determine whether it is the fish species or the breakdown of these prey that differ.

Tools in the animal kingdom

To date, the bottlenose dolphin of Shark Bay is the only cetacean known to use tools, a behaviour that is closely linked to culture, cognition and social learning. With the exception of humans, these individuals spend more time using tools than any other animal. Additionally, tool use for feeding on vertebrates is a behaviour that has only ever been recorded in these dolphins, chimpanzees and humans. Indeed, the use of tools is rather rare in the animal kingdom, having been documented in only about 30 species of birds, 10 species of primates and as few as 0.01% of all other mammals. The existence of this original and unusual behaviour in the Shark Bay bottlenose dolphin therefore raises a legitimate question: How did it come about in the first place?

Learn more

  • (2008) Mann, J., Sargeant, B. L., Watson-Capps, J. J., Gibson, Q. A., Heithaus, M. R., Connor, R. C., Patterson, E. Why Do Dolphins Carry Sponges? PLoS ONE 3 (12)
  • (2014) Krützen, M., Kreicker, S., MacLeod, C. D., Learmonth, J., Kopps, A. M., Walsham, P., Allen, S. J. Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiops sp.) provides access to a novel foraging niche. Proceedings of the Royal Society B 281
  • (2019) Wild, S., Allen, S. J., Krützen, M., King, S. L., Gerber, L., Hoppitt, W. J. E. Multi-network-based diffusion analysis reveals vertical cultural transmission of sponge tool use within dolphin matrilines. Biology Letters 15
News - 23/11/2023

Véronique Genesse

Véronique is a biologist and a writer for Whales online. She has discovered her love for cetaceans following memorable encounters with these giants of the sea. She then grew interested in conservation after becoming aware of the numerous threats they face. She believes that participation from the general public is essential for the success of conservation projects.

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