The moon is a powerful celestial body – influencing our ocean’s tides through its gravitational pull – and its mysteries have often been a subject in folklore and fantasy.
While its impacts on the tide are known, the moon’s many phases might also influence the creatures that swim within such as sharks, according to new research.
These ocean predators may attack more during fuller moon phases, including a full moon, a study conducted by Louisiana State University and the University of Florida suggests. Researchers analyzed international shark attack data gathered over decades, according to LSU’s Jan. 11 news release.
“More shark attacks than average occur during periods of higher lunar illumination and fewer attacks than average occur during periods of lower illumination,” the study, published in Frontiers in Marine Science, found.
Although researchers say they can’t pin down why phases of the moon might be related to an increase in shark attacks, they point out “this is the first global study to report an effect of lunar illumination on shark attacks.”
While it’s rare for a shark to attack a human, according to the National Oceanic and Atmospheric Administration, there were 57 unprovoked shark bites and 10 unprovoked fatal shark attacks in 2020 worldwide, according to the International Shark Attack File, which is the database analyzed in the study. The ISAF is based at the Florida Museum of Natural History at the University of Florida.
The study’s findings
Researchers say “all the instances of more shark attacks than expected occurred” when the lunar illumination was greater than 50% – meaning during a lunar phase when the moon had more light – and “all the instances of fewer shark attacks than expected occurred at lunar illumination of” less than 50%, researchers wrote.
They say there’s 100% illumination during a full moon, but no light at all during a new moon.
“It’s not a matter of more light at night for sharks to see. Most shark attacks occur in the daylight,” Steve Midway, one of the study’s authors and an associate professor at LSU, said in a statement.
“However, the moon can exert other forces on Earth and its oceans in ways that are much more subtle — for example, the gravitation pull that we see affect the tides.”
The study took a look at “confirmed unprovoked shark attacks from 1970-2016” documented by the ISAF and available data on moon phases from the U.S. Naval Observatory’s Astronomical Applications Department. Researchers also “sought to evaluate the co-factors of geography, shark species, and outcome of attack (fatal or non-fatal),” they wrote.
“Although our study finds statistical evidence for greater-than-expected numbers of shark attacks during lunar phases closer to the full moon, we cannot confirm a mechanism for this relationship,” authors say.
However, they say that “the moon’s effect on tides or electromagnetic fields” could influence the frequency of shark attacks during certain lunar phases and that the moon’s effect on shark attacks “may not be causative.”
They conclude that “although this is not firm evidence of shark attacks preferentially occurring during periods of greater lunar illumination,” it warrants “further investigation.”
Does the moon affect other animals?
The research on shark attacks says animal behavior “has been linked to the phases of the moon” before.
The moon’s activity can affect the circadian rhythm of both humans and animals, according to a study on the lunar cycle published in 2006.
Oysters and zooplankton are among other sea creatures that may also be affected by lunar phases, National Geographic reported.
“Moon phase is a well-established influence on animal behaviors, especially those in marine environments,” researchers from LSU and UF say.