70 Sharks: The Animal Answer Guide
Scalloped Hammerheads swim slowly above seamounts (small peaks in
the ocean’s floor) by day, in groups as large as 500 sharks. They disperse as
solitary individuals at night to feed, sometimes as far as 20 km (12 miles)
away and then return the next morning to the same seamount. The best-
known Scalloped Hammerhead aggregation is one that has been studied at
Espiritu Santo Seamount, off the coast of Baja California, Mexico.
Gray Reef Sharks also form daytime aggregations in Pacific atoll la-
goons. Dozens of animals may mill around in a small area inside the lagoon
or swim in place against currents in a lagoon pass during the day, stacked
up like logs along the walls of the pass. At dusk, they leave via the pass to
forage outside the reef, returning again the next dawn to the same daytime
resting locale. Daytime resting aggregations followed by nighttime disper-
sal are also common among bony fishes that feed at night on coral reefs and
in lakes.
Rays and skates are also mostly solitary animals. Exceptions include
some rays that rest in small groups on the bottom, such as Cowtail Sting-
rays (Pastinachus sephen) and Reticulate Whiprays (Himantura uarnak), as
well as myliobatid rays (Bat, Cownose, Spotted Eagle, and manta) that
swim up in the water column in groups of varying sizes. To the best of
our knowledge, which is admittedly limited, chimaeras are basically soli-
tary animals.
Do sharks form schools?
A school is a coordinated group of animals moving in the same direc-
tion at the same speed, often separated by a predictable but small distance.
By this definition, most sharks do not school, but a few definitely do. In
such schools, most individuals are of a similar size and the same sex, except
of course during mating, when many otherwise solitary sharks form large
groups of both sexes. Mating aggregations are discussed in chapter 6.
Among the best studied of the schooling sharks are Scalloped Ham-
merheads. Males tend to aggregate inshore, whereas females congregate
offshore over deeper water, sometimes in groups of several hundred ani-
mals. Female schools tend to mill around seamounts, rather than moving
continually in one direction. School Sharks, or Tope (Galeorhinus galeus),
often move in small schools composed mostly of individuals of the same sex
and age. Blue Sharks swim in groups segregated by sex even before the ani-
mals mature, with females staying nearer coastlines than males. Blue Shark
groups are usually small but sometimes occur in large numbers; as many as
1,000 Blue Sharks have been seen near the surface at the edge of the conti-
nental shelf off the coast of Maryland. By the strict definition of schooling,
these are more likely aggregations rather than true schools. Other species
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