Sea turtles, penguins, sharks and various marine mammals: they all swim in circles with remarkable frequency, according to data from modern tracking processes. What this apparently widespread movement pattern is all about remains a mystery so far. Depending on the species, there could be different functions. However, the circling may also have a superordinate meaning, speculate the marine biologists: It could be used for orientation to the earth’s magnetic field, so they suspect.
How and where sea turtles, dolphins and the like move in the vastness of the oceans has long remained largely hidden from science. But this has changed with the use of modern technology in marine biology. In addition to satellite-based monitoring, the movement patterns of some marine animals are now also examined using biologging technology. To do this, small measuring devices are attached to their bodies, the data of which scientists can then evaluate. This makes it possible to track the movements of marine animals in three dimensions and with high precision in time and space.
Biologging technology also led to the discovery of the phenomenon that the scientists working with Tomoko Narazaki from the University of Tokyo are now reporting on. First they found it in green sea turtles (Chelonia mydas) firmly. In order to investigate their navigation behavior in the event of disturbances, they equipped some test animals with biologists and transported them from one place to another. “I could hardly believe my eyes when I first saw the data. They showed that the turtles swam characteristic circular paths in the sea – as precise as machines, ”reports Narazaki. “I then reported this interesting discovery to colleagues who also used 3D data loggers for a wide range of marine megafauna species,” says the scientist.
Common phenomenon
In doing so, she attracted attention to the behavior – and so it finally became apparent that it was apparently a widespread phenomenon. “We have found that many different marine animals exhibit movement patterns in which they swim in circles more than twice in a row at a relatively constant speed,” reports Tomoko. She and her colleagues were able to document this behavior not only in sea turtles but also in penguins and in various species of sharks, seals and whales. As they point out, this finding is remarkable because swimming in a straight line is usually the most efficient way of getting around. So there seems to be a good reason why the animals swim in circles, the researchers say. As they explain, the similar application models could be based on different functions depending on the species – or there is a higher level of importance.
At first, it seems reasonable to assume that exercise behavior is primarily related to foraging for food. In some cases, the scientists also found evidence of this function. You notice, for example, that tiger sharks swim in circles in their hunting areas off Hawaii with a remarkable frequency. However, a meaning in the context of foraging is rather out of the question as a basic explanation, because there are too many examples in which this function does not appear plausible. In the case of seals and penguins, for example, it was found that they are more likely to behave when they are not hunting.
Orientation to the earth’s magnetic field?
“We therefore hypothesize that the circular movement patterns are linked to the investigation of the geomagnetic field,” the researchers write. As they explain, studies in recent years have shown that many marine animals use the geomagnetic field for directional information. In this context, the observations of sea turtles in particular provide indications of a function of circling in the context of orientation based on the earth’s magnetic field, say the scientists. “The results are remarkable, according to which the turtles swim in circles, especially at points that seem to be important for navigation, just before they start swimming,” says Narazaki.
Interestingly, submarines are also steered in a circle during geomagnetic investigations, as this enables a more precise measurement to be achieved by using measured values from all directions, the researchers emphasize. The scientists speculate that turtles, seals and co. With their largely unexplored magnetic perception systems could also investigate the geomagnetic field in order to orient themselves in the sea. As they emphasize, different explanations for the circular movement behavior are not mutually exclusive. For example, some animals could move in circles to improve their search for prey while gathering geomagnetic information.
Ultimately, according to the scientists, interesting research potential is now emerging: In future studies, Narazaki and his colleagues want to examine the circular movement patterns of various marine animals more closely. The focus is on the circumstances surrounding the behavior, which could provide clues as to what is actually behind the phenomenon.
Source: Cell Press, technical article: iScience, doi: 10.1016 / j.isci.2021.102221