The distribution of plankton tends to vary with the tide. Since tides
are most extreme during the full and new moon,
it is possible that moon phase also affects the distribution of
plankton, and accordingly the mantas that feed on
them. Thus, there is reason to believe that the
number of mantas observed in the bay may vary
with both the tide and the moon phase. The plots below show
how the number of mantas observed varies with
the moon phase (left) and daily tide (right). Individual days are shown
with dots. The angle at which the dot is drawn
around the origin indicates the moon phase or tide at the time mantas
were sighted, and the distance the dot is
drawn from the origin indicates the number of mantas observed.
More mantas are observed on rising tides and
in the period leading up to the new
moon (and to a lesser extent the full moon). On a rising tide
water flows into the bay. When this water
encounters an obstacle such as a patch reef or the sandbar, it is forced
toward the surface in a process called
upwelling. This concentrates plankton and other
particles in the surface waters near these
ledges, explaining both the increased feeding by mantas during
rising tides and the concentration of manta
sightings along the sandbar ledge. In the period around the
full and new moon tide are more extreme,
further concentrating plankton along the ledges.
Planning on visiting the bay in the near
future? Below is
a calendar heatmap to help you choose potential "good days" to try and
catch some mantas.
Darker colored days indicate that the average number of mantas seen on
that day of the lunar cycle
is higher than on lighter colored days. Good
luck!
