Pacific Islanders Weapons Indicate that Three Shark Species Disappeared

Carcharhinus-obscurus-spottail-shark

The analysis of the weapons used by the indigenous people of the Gilbert Islands in the central Pacific Ocean, which primarily use shark teeth, indicate that at least three species of shark have disappeared from the waters near the islands. Joshua Drew, a conservation biologist at Columbia University in New York, studied the weapons housed in the collection of the Field Museum of Natural History in Chicago, Illinois, and presented his findings at the 2012 Ecological Society of America’s Annual Meeting in Portland last week.

The people of the Gilbert Islands have been creating weapons from shark teeth for centuries. Drew used these teeth to show that the waters around these islands, which are part of the Republic of Kiribati, were once the home of three species of sharks that are no longer found in this area.

Carcharhinus-altimus-bignose-shark

Drew analyzed 124 shark-tooth weapons, which included swords, tridents and a 4-meter-long lance, dating back over 120 years. All of these weapons use a similar construction technique. Holes are drilled into them and teeth are lashed onto the buttresses of wood with cords made from coconut leaves. The teeth in one weapon usually come from the same species, but Drew found several blades which belong to a rare species of blue shark (Prionace glauca). This could have been a signature of a single artisan.

Sharks can be identified by their teeth, which allow these weapons to provide a clear record of the species that were once prevalent around the Gilbert Islands. Drew used field guides and high resolution photos to identify the teeth. The teeth came from 19 species of shark, and three of these, the spottail shark (Carcharhinus sorrah), dusky shark (Carcharhinus obscurus) and bignose shark (Carcharhinus altimus) are no longer found in the water close to the islands.

It is unclear why these species of sharks, which aren’t extinct, have vanished from the area, but humans may have played a role in the decline. There is a lack of good ecological data on shark populations before humans started to alter the ocean’s populations.

gilbert-islands-shark-weapon

[via Nature, images via Wikipedia]

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