Sharks and the full moon

Our article “Fishing during a full moon” has already indicated the discussion about whether moonlight might influence the behavior of fish. Now we have found a study, which was conducted by Australian scientists in 2013, who have examined the diving behavior of 39 gray reef sharks in Palau (an island country in the Pacific Ocean), namely with regards to environmental influences, like water temperature and also lunar happenings, in particular the full moon and the new moon. They tagged the sharks with transmitters and thus were able to measure where and how deep they dived during certain times.

The result says that sharks dive deeper during full moon nights as on other nights, however, during new moon nights less deep. Incidentally, this behavior has already been observed with sword fish and tuna. A possible explanation could be that smaller fish are persuaded by the moonlight to dive deeper in order to be better protected. Hence, predatory fish are forced to dive deeper as well to catch the prey and to be protected as well. To the contrary, during the new moon and the lack of light, the fish swim closer to the water’s surface

Further, the study shows that the diving behavior of sharks also depends on the water temperature. Fish begin to dive deeper in spring, because the water from the winter has then warmed up in deeper areas as well.

So this is how the Moon influences the behavior of animals. Once again it is evident that this is due to pure physical aspects, in this case the light.

Here is the original study for you to read:

Vianna GMS, Meekan MG, Meeuwig JJ, Speed CW.
PLOS ONE, 10.1371/journal.pone.0060331, April 10, 2013.
www.plosone.org