134 Sharks: The Animal Answer Guide
injected with dyes that stain hard structures, and then recaptured later.
Sometimes more than one ring is deposited in a year. One novel verifica-
tion method involves analyzing museum specimens that were alive during
the nuclear bomb testing period of the 1950s and 1960s, when radioactive
carbon was taken up by the animals alive at that time. A great deal has been
written about these and other aspects of age determination of sharks, most of
which appears in technical publications that an interested reader can explore.
The number of bands on vertebrae usually provide accurate counts. But
in some sharks, it matters which vertebrae are studied. In most lamnoid
sharks—such as Porbeagles, makos, and threshers—all vertebrae have the
same number of band pairs regardless of where on the body they are sam-
pled. But older Basking Sharks give different counts depending on which
vertebrae are used: vertebrae in the stomach region have as many as 24 more
band pairs then vertebrae near the tail (Basking Sharks have about 85 ver-
tebrae). Angel Sharks, Gummy Sharks, and School Sharks also have more
growth bands nearer the head than the tail. Researchers have interpreted
the differences to mean that bands are added to vertebrae to support the
body at that place along the shark, more bands providing greater support.
This means that in many sharks the number of bands is not a reliable mea-
sure of shark age.
The location on a fin spine where the bands are counted also makes a
difference. Chimaera spines give accurate age measures if ring counts are
made from the tip of the spine, but counts are unreliable if sections of the
base of a spine are studied. Also, fin spines can erode over time, obscuring
and even obliterating some growth rings.
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