56 Sharks: The Animal Answer Guide
each other apart, a useful feature during mating. These seemingly minor
patches of color are also helpful to people who are trying to tell sharks
apart. This is the case with the Porbeagle (Lamna nasus). Porbeagles differ
from all other lamnids because they have a distinctive white patch in the
lower rear portion of their first dorsal fin.
These variations in coloration are indicated by the common names of
many carcharhinid sharks: Blacktip Reef Shark, Blacknose Shark, Silver-
tip Shark (Carcharhinus albimarginatus), Whitetip Reef Shark, Whitenose
Shark (Nasolamia velox). It appears that such color is meant to be obvious.
The black tip on the dorsal fin of a Blacktip Reef Shark often has a white
lower edge, which makes the black tip stand out even more. The White-
nose Shark’s nose has a black tip with a white border behind the black, which
makes it a blacknose shark, but that common name was already taken.
Tiger Sharks, with their noticeable vertical barring (a color pattern that
fades with age) repeats a pattern seen in large bony fishes that often swim
near the surface, such as King Mackerel, Wahoo, tuna, and marlins. The
vertical barring is thought to mimic the flickering shafts of sunlight cre-
ated by ripples at the water’s surface, breaking up the outline of the fish and
making it harder to identify. This type of camouflage might also explain the
variably shaped white spots and lines on the backs of Whale Sharks.
Even more speculative are suggestions about the function of light color
on the fin tips of Oceanic Whitetips. The ends of the first dorsal, pectorals,
pelvics, and both lobes of the tail are distinctly white in this oceanic spe-
cies, which feeds on fast-moving offshore fishes. The idea is that an oth-
erwise countershaded shark approaching from a distance in open water is
almost invisible, except for the white tips. The tips are made even more vis-
ible by side-to-side tail movements and adjustments of the pectorals. A po-
tential victim could be fooled into thinking the obvious white marks were
something small and maybe even edible, allowing the Oceanic Whitetip
to get close enough to put on a burst of speed, when it was too late for the
prey to escape. If you watch videos of these sharks, or at least videos that
include footage as the shark approaches from out of the gloom, this idea
makes sense.
Finally, deepwater sharks—those that live well below the depth of sun-
light or moonlight penetration—tend to be uniformly dark in color. The
Portuguese Dogfish, the deepest living shark, is uniformly blue-black or
brown-black. This lack of patterning makes sense in terms of the assumed
function of countershading and its link to light distribution nearer the
surface: bright downwelling, intermediate spacelight, weak upwelling. In
the inky-black depths, light is equally absent in all directions. This makes
countershading, or any variation in color across the body, pointless.
Once again, known exceptions generally prove the rule. Some sharks
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