Crittercam Shows Sea Turtles Use Vision to Find Prey
A loggerhead with a Crittercam attached. Photo credit: Tomoko Narazaki (Atmosphere and Ocean Research Institute, The University of Tokyo)
“Never let a balloon go,” many teachers tell children. “They can end up in the ocean where sea turtles might mistake them for jellyfish and eat them.” It’s true. And now teachers will have video proof to show how something that looks like a jellyfish, but tastes like trash, can wind up in a turtle’s insides.
A new study conducted by researchers from the University of Tokyo and members of National Geographic’s Remote Imaging team (creators of the famous Crittercam) attached video cameras to loggerhead sea turtles swimming the ocean. The remarkable footage (downloadable here) shows encounters not just with jellyfish (which the turtles readily devour) but also with a plastic bag.
|A loggerhead turtle approaching a jellyfish (above) and a plastic bag (below). Photos from Nazaraki et al. 2013.|
The plastic bag encounter illustrates just how easy it is for a turtle to mistake a piece of trash for a tasty jellyfish. “The turtle’s movements while approaching the plastic bag were analogous to those of a true foraging event,” note the researchers—meaning that from afar, the turtle thought the plastic bag was a jellyfish. It’s only at the last second that the turtle turns away and decides the bag doesn’t look so appetizing after all. (Unfortunately, another study that examined the gut contents and feces of loggerheads found plastic and other man-made debris in nearly half of the turtles examined).
The study’s lead author, Dr. Tomoko Narazaki, hadn’t expected to see footage of a turtle encountering a plastic bag, and was “surprised and so excited” when he first saw the video clip. The study, which also used a device that recorded each turtle’s depth, speed, and 3-D movements, concluded that turtles mostly use sight, rather than smell or sound, to find their prey.
Predators that use smells to hone in on their next meal tend to move in a “zigzag” pattern as they figure out which direction the smell is coming from. But these turtles “maintained a straight-line course to approach the prey,” according to the study. Narazaki says that after their analyses, he “was convinced that turtles used vision.” But, he says, more research needs to be done to find out what cues turtles used to distinguish the plastic bag. With that knowledge, scientists might find ways to prevent turtles from a future shopping bag mix-up that could cost them their lives.