Bottlenose Dolphin Go Sponging

(c) Ewa Krzyszczyk / plosone.org

Wild bottlenose dolphins, given their widespread distribution across several ocean systems, display a wide variety of peculiar behaviors including carrying objects.  The question has remained, are these objects play things or is this carrying behavior an adaptive one that helps bottlenose survive?

For a subset of the bottlenose population in Shark Bay, Australia, sponge-carrying (or sponger) behavior isn’t play, its tool use!  Spongers, as they’re known, wear conical marine sponges over their rostrum and hunt along sandy bottom areas effectively disturbing sand-dwelling fish species that then streak across the sand, are spotted, and become lunch.

“[This is] one of the only suspected cases of tool use for any wild dolphin or whale, sponge-carrying (hereafter sponging) in Shark Bay, Australia, only 11% of adult female bottlenose dolphins (Tursiops sp.) carry marine sponges. Tool use in this population is striking compared to tool use in other species because of the degree of specialization, strong sex-bias, and matrilineal (vertical) transmission within a subset of the population. In addition, with the exception of chimpanzees and humans, habitual tool use to hunt vertebrates has not been documented.”

Even more intriguing is the “all or none phenomenon” that sponging presents for the species; animals either adopted this specialized strategy or not.  Researchers suggest that the considerable time commitment required for successful sponging limits its adoption by dolphins outside of the matrilineal line (where female calves appear to regularly adopt the practice from their mothers).  In fact, “spongers devote more time to using tools than any non human species”.

If only Florida’s resident bottlenose would adopt fascinating tactics like this one! 

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