Foods and Feeding 149
pads; Whale Sharks have widely spaced, flattened filtering pads; mantas
possess rigid, leaflike, folded pads; and Megamouth Sharks have furlike,
short gill rakers.
Basking and Whale sharks and manta rays swim with open mouths, em-
ploying what is commonly called “ram feeding.” This means that water is
forced through the mouth and out the gill slits by the forward motion of
the animal, an action that serves to continuously trap zooplankton on the
filtering pads. All swim slowly, between 0.5 and 1 m/s (roughly 1–2 mph).
Megamouth Sharks rely more on suction to draw water in, which is then
forced back by closing the mouth. Filter feeding has also led to a very basic
change in the mouth location compared with most sharks: Megamouth and
Whale sharks and manta rays are among the half dozen chondrichthyans
whose mouth is located at the front of the head rather than below it.
Basking Sharks feed as individuals at low plankton densities, but when
they encounter high concentrations of food, they form lines of feeding
sharks. Each shark drops and spreads its lower jaw to create a circular hoop
that can be a meter (3 ft) across. The shark swims slowly, thus posing for
what has become the classic Basking Shark feeding photo (usually taken
of sharks feeding at or just below the surface). Plankton is caught on the
bristlelike pads. The bristles have a microscopic, 0.8-mm (0.03-in) gap be-
tween them that traps food but allows water to pass. The shark closes its
mouth, backflushes the gill rakers, and then swallows.
Whale Sharks also feed individually or in groups near or at the surface.
They have a more varied feeding repertoire than Basking Sharks. They
may ram-feed much like baskers while swimming slowly, at about the same
speed as baskers, but with the upper jaw out of the water. They can also stop
and suck water in and out in pulses, the method they commonly use when
fed in captivity (such as in very large public aquariums). An additional tech-
nique involves rising vertically out of the water and then sinking quickly
back, making water and prey flow into their open mouths. Food is caught
by mesh-covered pads that fill the mouth and throat, attached to the inside
of the gill filaments. Whale Sharks occasionally “cough” as an apparent
way to backflush and then swallow organisms and eggs trapped on the pads.
Mantas are the most active of the plankton feeders, foraging along the
bottom as well as up in the water column. They appear to fly through the
water, slowing as they encounter patches of prey, twisting, turning, and
somersaulting (“barrel rolling”) backwards to stay in concentrated patches.
Unlike the others, mantas will also feed just above the bottom. They fun-
nel plankton-bearing water into their mouths and out their gill slits by ex-
tending their “horns” in front of them. The horns are forward extensions
of their pectoral fins, making them the only vertebrates with three pairs
of paired limbs. Food is trapped by mucous that covers modified toothlike