Marine Science/ Per. 1
recognizable of all the sharks. The Hammerheads are among the strangest looking
sharks. As the name indicates they have a flattened head which resembles the
head of a hammer. Their eyes and nostrils are at the ends of the hammer. There
are many species of Hammerheads. There are eight living species of hammerheads.
The following four are the main categories:
1. Scalloped hammerhead (Sphyrna lewini)-Pectoral fins are tipped with black
this grey shark. The maximum length is about 12 feet.
2. Bonnethead (Spyrna tiburo)-With a head shaped like a shovel the bonnethead
3. Smooth hammerhead (Sphyrna zygaena)-Bronze with dusky fin tips, it can grow
to thirteen feet.
4. Great hammerhead (Sphyrna mokarran)-Attaining a length of a possible 18 feet,
this is the largest and most dangerous of all the hammerheads.
One of the most interesting things about the hammerheads is the unique
they have speculated about the use of the hammer. The hammer is a complex
structure and probably serves more than one function. The most important
function of the hammer according to scientists is increased electroreceptive
remarkable sensory ability to detect the small electrical auras surrounding all
living creatures. Under certain conditions, such as in searching for wounded
animals, the electrical activity increases helping the hammerhead to feed. It
is also believed that the hammerhead may be able to use the Earth’s magnetic
field as a source for navigation. Some hammerheads migrate a lot and may rely
the hammer is to enhance maneuverability. The hammer’s similarity to a
hydrofoil seems to explain its usefulness for maneuverability and improved lift.
However, this theory has not been tested.
Among sharks hammerheads have a relatively large brain-body weight ratio.
Sharks differ form most other fish in several ways. Sharks have a boneless
skeleton made of cartilage that is a tough elastic substance. Most sharks have
a rounded body shaped like a torpedo. This shape helps them swim efficiently.
All sharks are carnivorous. Most eat live fish, including other sharks.
Most sharks eat their prey whole, or tear off large chunks of flesh at a time.
They also eat dying animals. Hammerheads have definite food preferences. Their
elongated head may help them locate the prey they prefer. The Great Hammerhead
difficult to detect because they are partially buried in the sediment. Yet, the
hammerhead is capable of finding them because they can swim close to the bottom
swinging their heads in a wide arc like a metal detector.
Sharks reproduce internally. Unlike most fish sharks eggs are
fertilized internally. The male shark has two organs called claspers which
release sperm into the female where it fertilizes the egg. In many sharks the
eggs hatch inside the female, and the pups are born alive. Other species of
sharks lay their eggs outside. The hammerhead female has an internal pregnancy
in which a placenta is formed around the embryo. The gestation period for most
placental sharks is between nine and twelve months. The placenta appears about
two to three months after ovulation when the embryos have consumed their yolk.
Eggs are ovulated at intervals of a day or so, which explains why their may be
considerable variations in the developmental ages of pups in a litter. It’s not
unusual to find embryos that have died during development.
Hammerhead sharks tend to form schools of fifty to two hundred. They
tend to congregate and swim at special sea mounts. Sea mounts are underwater
mountains. In these sea mounts there are many other fish attracted by rich
algae and invertebrate larvae. The hammerheads have no interest in these fish.
sea mounts show that the majority of hammerheads there are female. This
indicates that its easy for the male to find a mate. However, researchers were
surprised to find that there were many immature female hammerheads at the sea
mounts. This led them to believe that in addition to reproduction there must be
serve as navigational centers. Each evening the hammerheads begin a ten to
The young females participate in these long distance swims. The sea mount
serves as a navigational center helping them find their way back. The nightly
swim help the young find nutritious food which helps them in their growth.
Klimley, Peter, “Hammerhead City”, Natural History, Oct. 1995, pp 33-38. Martin,
Richard, “Why the Hammerhead?”, Sea Frontiers, May-June 1989, pp. 142-145. Moss,
Book Inc., 1988.