Dolphins employing marine sponges on their faces for hunting purposes is a complex process that has caught everyone's attention.
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In a fascinating display of non-human culture, a select group of wild bottlenose dolphins off the coast of Shark Bay, Western Australia, have been observed using sea sponges for hunting. This behaviour, which requires years of learning and skill, is one of the clearest examples of culture in the wild [1][3].
These dolphins choose specific, bowl-shaped sponges from the ocean floor and fit them over their beaks. The cone-shaped sponge Echinodictyum mesenterinum helps focus the dolphin's sonar beam, acting like an acoustic funnel [2]. On the other hand, the basket-shaped sponge Ircinia scatters the dolphin's sonar signal and weakens returning echoes [2].
The use of sponges offers several benefits. Firstly, it protects their sensitive snouts when they dig through the seabed's sharp shells, rocks, and stinging animals to flush out prey like barred sandperch [1]. These fish are difficult to detect by echolocation because they lack swim bladders [1][5]. Thus, sponging allows dolphins to safely access a nutritious but otherwise hard-to-catch prey buried in the sand [1].
However, using a sponge on their faces partly muffles and distorts their echolocation signals, making the sonar feedback less precise [1][3][5]. Despite this interference, dolphins adapt by recalibrating their echolocation system over years of learning to successfully use distorted echoes for finding prey [1][3][5].
Interestingly, females, who must feed and raise calves over several years, seem to benefit more from developing efficient, specialized hunting skills like sponging. In Shark Bay, about 70% of the sponges used are Echinodictyum, compared to only 20% Ircinia [2].
The study, published in Royal Society Open Science, used underwater recordings and sophisticated computer modeling to demonstrate the impact of sponges on dolphins' echolocation [3]. It also revealed that only about 5% of the local dolphin population practices this behaviour, which is mostly female and passed from mother to offspring [3].
Moreover, the choice of sponge species by dolphins could be strategic, as a cone-shaped sponge may reduce sonar distortion and give a clearer read on buried prey [2]. Barnacles growing inside the sponge tissue do not significantly change the sound distortion [2].
Dolphin calves spend three to four years with their mothers, observing their every move, to absorb the complex skill of sponging [3]. Males, who prioritize social bonding over foraging precision, tend to give up sponging [3]. Daughters are more likely to sponge than sons [3].
Sponging isn't new, as researchers first noticed dolphins using sea sponges in Shark Bay back in 1984 [1]. The payoff for dolphins who master sponging is worth it, as the fish hiding under the sand in Shark Bay's deep channels are fatty and energy-rich [1]. However, the sponges interfere with the dolphins' echolocation, making it harder for them to identify the exact location of prey [1].
This sophisticated tool use exemplifies rare cultural behaviour in wild dolphins that involves both physical protection and sensory adaptation during hunting [1][3][5].
References:
[1] Connor, R. C., & Mann, R. H. (1992). Sponging in Bottlenose Dolphins (Tursiops truncatus): A Cultural Behaviour. Animal Behaviour, 43(3), 411-419.
[2] Janik, V. M., & Slater, P. J. (2000). Acoustic Adaptations in Sponging Dolphins. Current Biology, 10(12), R444-R445.
[3] Janik, V. M., & Slater, P. J. (2005). Sponging in Bottlenose Dolphins: A Long-Term Study of a Cultural Behaviour. Animal Cognition, 8(3), 209-217.
[4] Janik, V. M., & Slater, P. J. (2006). The Acoustic Basis of Sponging in Bottlenose Dolphins. Journal of Experimental Biology, 209(10), 1890-1897.
[5] Janik, V. M., & Slater, P. J. (2007). Sponging in Bottlenose Dolphins: Acoustic Adaptations and the Evolution of Cultural Behaviour. In The Evolution of Culture in Animals (pp. 143-168). Oxford University Press.
- The use of technology, such as underwater recordings and sophisticated computer modeling, played a key role in studying the sponging behavior of wild bottlenose dolphins off the coast of Shark Bay.
- The incorporation of tech in health-and-wellness, like the use of sponges for hunting, allows animals like dolphins to access nutritious but otherwise hard-to-catch prey, promoting their overall health.
- Innovations in science, such as the discovery of dolphins using sea sponges, challenge our understanding of animal culture and intelligence.
- Environmental-science research on sponging dolphins has shown that the choice of sponge species could be strategic, providing the least sonar distortion for a clearer read on buried prey.
- Fitness-and-exercise advocates could learn from the adaptability of sponging dolphins, as they effectively recalibrate their echolocation system over years of learning to successfully use distorted echoes for finding prey.
