- Many marine animals are intentionally swimming in circles consecutively at a relatively constant speed more than twice, according to a new study using data from movement trackers.
- The researchers say the behavior is surprising in part because swimming in a straight line is known to be the most efficient way to move about.
- They found some of the animals swim in circles during different activities, including foraging, courtship, navigation and even possibly geomagnetic observations.
Many marine megafauna share a similar behavior of swimming in circles, often when in search of food, but also while engaged in a range of other activities, according to a recently published paper.
Green sea turtles, sharks, penguins, and marine mammals tend to circle consecutively at a relatively constant speed more than twice, according to the study published March 18 by a group of researchers from Japan, Italy, France and the U.S. in the journal iScience.
“We have been studying behaviours and ecology of marine megafauna. But there are still lots of mysteries,” lead author Tomoko Narazaki, a marine scientist from the University of Tokyo, wrote in an email to Mongabay.
The researchers found that some of the animals, which were fitted with movement trackers, would swim in circles during different activities, such as foraging, courtship, navigation and even possibly geomagnetic observations. They noted that the behavior was surprising in part because swimming in a straight line was considered to be the most efficient way to move about.
The paper said that while circling behavior occurred primarily during active swimming, some circling might occur passively, as observed in northern elephant seals (Mirounga angustirostris), which would fall in a spiral manner during inactive drift phases of resting dives.
Potential explanations for circling behavior discussed in the paper are not mutually exclusive, the authors note. They said some animals might move in circles to enhance prey search while simultaneously collecting geomagnetic information. Others, such as elephant seals drifting down like falling leaves, might maintain directional sense by geomagnetic scanning while resting in seemingly featureless mesopelagic depths.
“There were a few papers describing circling movements in single species … But, our paper is the first study to report that many marine animals showed similar circling movements,” Narazaki said.
The team first discovered this circling movement in green turtles while examining their navigation ability during an experiment using dead reckoning to track 3D movements of free-ranging marine animals, according to Narazaki.
When she noticed the unusual behavior, Narazaki reported it to her colleagues who then used the same 3D data loggers to study a wide range of marine megafauna taxa.
“High-resolution 3D data loggers enable us to examine fine-scale underwater behavior that has been overlooked in previous studies,” Narazaki said.
Narazaki said her team’s study opens up opportunities for further research into marine animal behavior using other advanced technologies, for instance integrating high-resolution 3D movement data loggers and satellite telemetry to examine detailed movements over longer tracking periods.
The understanding of sea animals at such a fine scale, such as circling movement or other behaviors, will significantly benefit effective conservation of the marine ecosystem at large, Narazaki said.
“It is important to note that there are so many unknown behaviors and/or impacts derived from human activities,” she said.
Narazaki, T., Nakamura, I., Aoki, K., Iwata, T., Shiomi, K., Luschi, P., … Sato, K. (2021). Similar circling movements observed across marine megafauna taxa. iScience, 102221. doi:10.1016/j.isci.2021.102221
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