72 Sharks: The Animal Answer Guide
But within these groups, can sharks identify different individuals? Be-
havioral studies have shown that certain sharks and rays occur or reap-
pear at the same place for months or even years, often together with the
same individuals. Examples include White Sharks at the Farallon Islands
near San Francisco, at Guadalupe Island in Mexico, and near Cape Town,
South Africa; Small-spotted Catsharks and Port Jackson Sharks in daytime
resting caves; Sicklefin Lemon Sharks in Tahiti; Blacktip Reef Sharks in
Moorea, French Polynesia; Whitetip Reef Sharks in Hawaii; Zebra Sharks
in Queensland, Australia; Whale Sharks in the Maldives; Spotted Eagle
Rays at Bimini in the Bahamas; and Reef Manta Rays in Mozambique.
Researchers identify individuals using natural marks on fins, colored
spots and scars on the body, fin tears and notches, or distinct color patterns.
For example, in Blacktip Reef Sharks the relative size and shapes of the
black, brown, and white patches at the tip of the dorsal fin differ among in-
dividuals. Individual Zebra Sharks have unique color patterns, and Spotted
Eagle Ray individuals have unique spot patterns. Photos over many months
show that the differences are long-lasting, identifiable for up to a 10-year
period in Blacktip Reef Sharks. In some species such as White Sharks, the
accuracy of the identifying marks has been confirmed with genetic finger-
prints. This allows researchers to accumulate photo albums of individuals
and follow them through time, as has been done for humpback and killer
whales.
Do the sharks also tell one another apart? This is a harder question to
answer than simply asking if the same animals occur together repeatedly.
Some evidence suggests that sharks are capable of selecting the sharks they
associate with, at least when kept in captivity in small numbers. Female
Small-spotted Catsharks kept in small groups in laboratory tanks tended
to associate with particular individuals and avoided others. Their behavior
changed notably when unfamiliar females were introduced into a group,
again suggesting that they knew who was who. Whether similar behavior
in this species occurs in the wild is unknown. Observations of 38 wild juve-
nile Lemon Sharks at a known aggregation site at Bimini, Bahamas, indi-
cated that certain individuals tended to associate preferentially with other
individuals. Pairs tended to be made up of similar-sized animals, regardless
of sex, which could be individual recognition or just a preference for asso-
ciating with an animal of the same size. Researchers watched from nearby
towers and could tell individuals apart because the sharks had been tagged
with color-coded tags.
More definitively, a careful study of a population of 133 Blacktip Reef
Sharks in Moorea demonstrated that the population was divided into four
subgroups of 14 to 54 individuals per group. Individuals within the groups
tended to pair with some individuals and avoid others, with animals of a
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