Sharks, Turtles, and Penguins Are All Swimming in Circles. No One Knows Why.

Could it have something to do with Earth’s magnetic field?

  • A new study shows marine animals swim in circles, and scientists are baffled.
  • Some circles are likely navigational, while others are for feeding.
  • Animals studied range from whales to sharks to penguins, making this a widespread behaviour.

Scientists have discovered a confounding pattern in nature: Many marine animals are strangely swimming in circles

The researchers modeled the animals’ behavior using a variety of math ideas and the navigational concept of dead reckoning. In a variety of animals, including turtles, penguins, and a solitary whale shark, the scientists spotted the behavior because of the advent of true 3D sensing of movement. 

Why is this happening? No one is exactly sure.

Lead study author Tomoko Narazaki, of the University of Tokyo, first noticed the circles in a group of turtles she was studying, according to Vice. She and her team moved the turtles specifically to monitor how they would navigate back to their home waters, and even with a destination in mind, they still often swam in circles. Surprised, Narazaki encouraged her colleagues who studied different animals to look at their sensor data as well.

“Examining high-resolution 3D movements of sharks, sea turtles, penguins, and marine mammals, we report the discovery of circling events where animals consecutively circled more than twice at relatively constant angular speeds,” Narazaki and her coauthors write in their study, which appears in iScience.This content is imported from {embed-name}. You may be able to find the same content in another format, or you may be able to find more information, at their web site.

(A) Tiger shark, (B) Whale shark, (C) King penguin, (D) Antarctic fur seal, (E) Green turtle, (F) Cuvier’s beaked whale. The movement of a submarine during geomagnetic measurements is also shown in (G). The shaded area in (F) is displayed three-dimensionally in (H) showing how a Cuvier’s beaked whale circled during final ascent phase of a deep dive.Source: Narazaki et al., Similar circling movements observed across marine megafauna taxa, iScience (2021)

The scientists gathered the data while the animals—located everywhere from the Cape Verde Islands to Okinawa, Japan—were foraging, swimming home, and returning after nesting. The circles ranged from just a few to dozens in a row. The scientists saw most of the recorded circles during foraging, especially among the sharks:

“For example, a total of 272 circling events were observed in four tiger sharks tagged off Hawaii. Sharks circled 2–30 times at wide-ranging depths but maintained relatively constant depth during each circling event. In addition, circling behaviours previously reported in bottom-feeding sandbar sharks occurred primarily close to the seafloor, suggesting a role in foraging.”

But feeding isn’t the only possible explanation for circling behaviors. “[M]any circling events appear unrelated to foraging,” the researchers report. “For example, a shark-mounted video showed a male tiger shark circling to approach a female for courtship.” And seals circled during the day when their primary foraging time was at night.

The study team suspects the circling of many animals has to do with navigating using the Earth’s magnetic field. The researchers explain: 

“Animals might also be able to improve measurement accuracy by taking multiple samples by circling several times. Animals might circle to derive directional/positional cues from the geomagnetic field, especially in navigationally challenging situations.”

In the study, some animals were equipped with sensors and GPS tags, while the scientists themselves observed others. The technology to monitor animals this way, and humanely, is still very new and growing. The scientists say the ideal next step is to record a lot more data and analyze it in a simultaneous way to help identify patterns.

Source: Popular Mechanics