Franciscana, or La Plata River, dolphins are only found in waters off the coasts of Argentina, Uruguay and Brazil. According to the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species, its population is threatened. That's because hundreds of the slender dolphins drown in fishing nets along the coast of South America every year. Scientists have developed this so-called "banana pinger," a high-frequency transmitter that's attached to fishing nets and scares dolphins away.