© Narazaki et al. / iScience
This image shows the circling behavior of various marine megafauna.
Technological advances have made it possible for researchers to track the movements of large ocean-dwelling animals in three dimensions with remarkable precision in both time and space. Researchers reporting in the journal
iScience on March 18 have now used this biologging technology to find that,
for reasons the researchers don't yet understand, green sea turtles, sharks, penguins, and marine mammals all do something rather unusual: swimming in circles.
"We've found that a wide variety of marine megafauna showed similar circling behavior, in which animals circled consecutively at a relatively constant speed more than twice," says Tomoko Narazaki of the University of Tokyo.
Narazaki's team first discovered the mysterious circling behaviors in homing green turtles during a displacement experiment. They had transferred nesting turtles from one place to another to study their navigation abilities.
"To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine!" Narazaki says. "When I got back in my lab, I reported this interesting discovery to my colleagues who use the same 3D data loggers to study a wide range of marine megafauna taxa."
What came next surprised the researchers even more: they realized that various species of marine animals showed more or less the same circling movements. This finding is surprising in part because swimming in a straight line is the most efficient way to move about. It suggests there must be some good reason that animals circle.
Comment: Tiger attacks on people skyrocket in the Sundarbans, India - 70 in 3 months with 40 deaths