Marine Tool Users

Date: 1/10/2011

Australia’s Shark Bay dolphins likely turned to gadgetry because echolocation couldn’t find the best fish. Researchers observed dolphins fitting basket sponges over their beaks, and then scraping through seafloor mud to disturb hidden fish. Though sponges clearly protected sensitive dolphin snouts from jagged pieces of rock and coral, why scrape seafloor at all?

Most fish scared from the muck were bottom-dwellers lacking swim bladders, the air-filled organs that help fish control their buoyancy. Compared to fish flesh, which interferes with acoustic signals just slightly more than water, air bladders stand out on sonar. Without them, bottom-dwelling fish are nearly invisible to echolocation. Hence the value of scraping through seafloors manually and thus the need for a device that protects dolphin noses from scraping.

Hunting with sponges allows Shark Bay’s bottlenoses to fill an empty ecological niche, eating fish that other dolphins ignore. The findings also suggest why sponge foraging likely arose among Shark Bay’s females and has remained their province, taught by dolphin mothers to daughters rather than sons. Dolphin moms spend years with their calves. Sponge foraging is convenient and nutritious, a family recipe for quick-but-delicious dinners passed on to daughters

who will someday need it.

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