Davi de Oliveira Moreira, known as "Sereio" (merman in Portuguese), poses in costume at Arpoador Rock on Ipanema Beach in Rio de Janeiro, Brazil, last May.
Yasuyoshi Chiba/AFP/Getty Images
Marine ecologist Neil Hammerschlag says he can sometimes identify sharks like Emma (pictured) by the way they move. "It's pretty cool to be able to jump in the water and say, 'Hey look, there's Emma the tiger shark!' "