38 Sharks: The Animal Answer Guide
trast. Shark coloration—or rather, the lack of it beyond bold darks and
lights—supports this conclusion. Skates also apparently have only rods in
their retinas.
Rays and chimaeras are different from sharks. Some have three cone
types, suggesting they can discriminate among colors. This makes sense
given that some rays have colors such as blue spots and live in shallow
water where all wavelengths of light penetrate. Freshwater stingrays and
the Bluespotted Stingray, Dasyatis kuhlii, are striking but not the only ex-
amples. The Bluespotted Stingray has the necessary three types of cones
in its retina that should enable it to see colors, as does the Yellow Stingray,
Urobatis jamaiciensis. At least one chimaera, the Australian Ghost Shark,
Callorhinchus milii, has three cone visual pigments and therefore could have
color vision. Some chimaeras (such as the Pointy-nosed Blue Chimaera,
Hydrolagus trolli) are reddish or purplish, but red light does not penetrate
to the depths where most chimaeras normally live, which means their bod-
ies would appear black. But even some of these deep-living species migrate
to shallow areas to spawn, so perhaps color vision comes into play at that
time. Once again, chimaera biology is full of mysteries.
What about sharks’ seeming preference for yellow? Researchers at-
tached baits to different colored floats. They found that sharks preferred
baits tied to international orange floats. Life jackets are often this color
because we see it well. Combining life jacket color with shark feeding pref-
erences has prompted Navy experimenters to call the color “yum-yum yel-
low.” (See the MythBusters episode “Sharks Prefer Yellow?” MythBusters
gave the yum-yum yellow idea “plausible” status.) But this attraction could
be to brightness rather than the color itself.
Although the new research on shark color vision looked at only 17 of
the 400 or so shark species, it strongly suggests that sharks are color blind.
A shark may be able to smell small amounts of blood in the water, but it
doesn’t know that it’s red.
How do sharks detect electric fields?
In addition to the conventional five senses of touch, taste, smell, vision,
and hearing, sharks have a sixth sense that we (and all mammals except the
duckbill platypus) lack. Sharks, rays, and chimaeras can detect weak elec-
tric fields, or at least they all have the Ampullae of Lorenzini that are the
electrosensory structures responsible for detecting such stimuli in species
known to detect weak electricity.
An ability to detect electrical fields aids sharks in finding nearby food,
and in fact when a shark finally homes in on a food source, information
from the electrical output of the prey may be more important than its
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