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Horn Sharks. Heterodontidae species.
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protected: © 2002 Kelvin Aitken.
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Probably the most well known of the eight species of Horn Shark is the
Port Jackson Shark (Heterodontus portusjacksoni), named after a bay in
eastern Australia. Port Jackson Sharks are one of the most common sharks
seen in southern Australian waters, especially in New South Wales. This
species ranges from southern Queensland around the southern States to
Geraldton in Western Australia. Port Jacksons have a distinctive bulky,
blunt head with a "pursed" mouth. They are usually grey in colour
with tints of brown or green, and a black-banded pattern on the body similar
in shape to the harness worn by a seeing-eye dog.
Female Port Jackson sharks may travel as far as 850 km to lay their eggs
among shallow rocky reefs during late winter and spring. These spiral-shaped
eggs are a dark green or brown when new but soon become almost black and
are usually encrusted with spots of algae. Females are supposed to push
their eggs into crevices but they are wedged in by wave action. Eggs that
have been left in the open or torn loose by storms are often found washed
ashore. The young pups that hatch 10–12 months later are about 15–20
cm long at first but they grow to 1.5 m or more.
Divers and snorkelers may come across Port Jackson Sharks, sometimes in
groups of 10–20, lying in sheltered caves or gullies on shallow rocky
reefs during the day. Here they sleep or rest until the night when they
disperse to feed on sea urchins and shells. Their scientific name, Heterodontus,
means 'different teeth' and refers to their spiky front teeth, which are
ideal for prying and holding; the fused teeth-plates at the rear are perfectly
developed for crushing shelled molluscs.
Crested Horn Sharks (Heterodontus galeatus) are only found on the east
coast of Australia in a confined region from southern Queensland to Montague
Island. Similarities with the Port Jackson are their teeth, diet and body
shape. They can be best distinguished from the Port Jackson shark by the
larger crests above the eye and the lack of a harness-shaped pattern on
the body, having two indistinct dark bands or 'saddles' over a yellowish
brown base colour instead. They also have rounder dorsal fins and do not
congregate in groups.
Reproductive behaviour is very different from that of the Port Jackson
Shark. Females lay spiral-shaped egg cases with long sticky tendrils up
to 2 m long. The female chooses a section of reef, often where other females
have already deposited their eggs, and tightly circle a suitable vertical
projection, such as sea tulips, kelp or a rock. As she rubs her body against
the reef the sticky tendrils, which have emerged slightly from her body,
become attached, pulling out the egg cases as she swims away. The eggs
are anchored to the reef by the well-tangled tendrils. Eight months later
the 20–22 cm young emerge to grow to their adult size of 1.5 m
The Zebra Horn Shark (Heterodontus zebra) is found in the Indo-Pacific
being more common in Asian seas. Their name comes from the striking pattern
of dark vertical stripes on a pale background.
Other species of Horn Shark include the Californian Horn Shark (Heterodontus
californicus) and the Mexican Horn Shark (Heterodontus mexicanus)
Horn sharks can be sent into a state of trance-like ecstasy by gently
scratching their bellies and throats. However these docile sharks should
not be handled as their robust dorsal spines can inflict a painful wound
and their crushing teeth can mash a wayward finger.