132 Sharks: The Animal Answer Guide
How fast do sharks grow?
Sharks grow throughout their lives, rapidly at first, then at slower and
slower rates as they age. Taking the White Shark as one example, a new-
born White Shark female is about 1.5 m (5 ft) long. At two years old, she is
about 2 m (6.5 ft) long, having increased 33% in one year. By the time she
reaches maturity at around 5 m (16.5 ft) long, she is likely to be a 14-year-
old teenager. During the initial growth phase, White Sharks feed primarily
on fish and grow slowly. Growth accelerates when the teeth become trian-
gular and the diet often changes to calorie-rich marine mammals, which
occurs at between 3 and 4 m (10–13 ft) in length. In large adult White
Sharks, growth slows considerably, an animal increasing by only about 6%
of its total body length per year, although weight and girth may increase at
a greater rate.
Growth in different species will vary by locale, sex, stage of develop-
ment, and diet. Growth rates are known for a number of chondrichthy-
ans, the results usually reported as percentage increase in body length each
year. Evaluating these and other available numbers, we can conclude that
male chondrichthyans grow at an average rate of about 20% per year, and
females grow at the same or a slightly lower rate, with many exceptions.
How can you tell the age of a shark?
Researchers study the few hard parts of sharks to determine their ages.
Growth rings of calcified cartilage and proteins are laid down regularly
on hard structures such as fin spines on Spiny Dogfish, Horn Sharks, and
chimaeras, and on tail thorns of skates. Scales can be used to determine the
ages of bony fishes but not for sharks because sharks shed their scales regu-
larly. The “bony” barbs of stingrays can’t be used for the same reason.
When magnified or x-rayed, thin sections sliced from spines or the
backbone of a shark show dark and light bands that represent slow and fast
growth in cold and warm seasons, much like tree rings. The dark lines oc-
cur where the added layers are close together owing to slow growth, such
as in winter. The light lines are the layers that were added much faster, as
during the summer. Each pair of rings should represent a year’s growth,
except in tropical species, which don’t necessarily face predictable seasonal
periods of slow and fast growth.
The age and growth of a great number of shark, ray, and skate species
have been described from the vertebral banding patterns of animals caught
at sea. Results are sometimes uncertain because it is difficult to determine
if a band pair truly represents one year’s growth, something that has to be
verified from studies of captive animals or animals that have been caught,
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