Reef manta rays are large filter feeders that
are found in coastal waters across the tropical Indian and Pacific Oceans.
Though they are closely related to sharks and can grow to a massive wingspan
of 15 feet, mantas only eat plankton and small
fish. They take in large volumes of water through their massive
mouths, and filter the water through their gills to sieve out these small
organisms.
Mantas can be found across the Hawaiian islands. On the island of Oahu, one
hot spot for them is Kāne'ohe Bay, a large sheltered bay off the eastern
shore. The waters of Kāne'ohe Bay have lots of
nutrients, which provides abundant plankton for mantas but also
causes water visibility to be very poor.
Unfortunately, very little is known about the mantas
that inhabit Kāne'ohe Bay. They have been observed feeding in
groups of up to nine individuals. When the group encounters an area rich in
plankton, they rotate around the area to concentrate the plankton, then
swoop in to feast. This is thought to be a more efficient way to feed than
acting individually.
A simple study was carried out to learn more about the
distribution and abundance of mantas in Kāne'ohe Bay. A drone and
paddleboard were used to survey a portion of the bay, and all mantas
encountered were recorded. This provided data on the location and group size
of mantas, as well as several environmental factors that could affect the
behavior of mantas. Photos of the mantas, both from air and in water, were
taken for later reference.
