Hammerheads tend to be known for their namesake,
i.e. that insanely shaped noggin. There are ten species of hammerhead sharks with Carolina
hammerheads being the most recently discovered back in 2013. Bonnethead sharks are included
as hammerhead sharks and all ten species belong to the Sphyrnidae family. That iconic
hammer shape is referred to as a cephalofoil and there are a couple of reasons why
these sharks may have developed this way. With their eyes positioned at the tips of
their face, hammerheads are allowed a 360 degree vertical view of their world meaning they
can keep a pretty close eye on potential meals. Of course, this does mean that they are a bit
lacking in having the ability to see right in front of them. They make up for this with sensory
organs called ampullae of Lorenzini which are also found in other cartilaginous fish. The ampullae
of Lorenzini are used to detect electric fields in the water. All living organism give off some sort
of electric field and hammerhead sharks are able to pick up on that. Plus, with a wider head, it’s
possible for them to have more receptors and thus be more sensitive to the movements of their prey.
This helps them in finding their favorite food: rays.
Although rays tend to spend time hidden
beneath the sand, hammerheads are able to detect their electric fields and scoop them from the sea
floor. They’ll even use their hammer-shaped head to hold prey down while they eat because
their mouths are actually pretty small. While hammerhead sharks prefer rays, they also
eat other fish, squid, octopus and even each other from time to time. There has even been some
controversy over whether or not some species of hammerheads eat sea grass. Bonnetheads have been
observed consuming seagrass and digesting up to 56% of the organic matter found within. Still,
they’re not sure whether or not this is actually helping to sustain these sharks or if it’s just
a learning curve of hunting as they tend to find young sharks with more seagrass in their diet than
more experienced, older sharks. Larger species of hammerhead, such as the great hammerhead, are
more likely to eat smaller sharks than the smaller species.
However, smaller hammerhead sharks do
something pretty amazing to help combat this. A behavior rarely observed in any other shark
species, hammerheads form schools up to 500 individuals. It’s still not entirely understood
why this takes place but something odd to note about this is that they tend to only school during
the day. At night the sharks will disperse and go off to hunt on their own. Some suggestions for
why this happens are that it is for protection because, as mentioned previously, it tends to
be the smaller sharks schooling while larger hammerheads tend to travel alone. It could also
be used for protection during the mating season. A lone female may be bombarded by a
wondering drove of male hammerheads, but with a group the female has more
options to be picky. Safety in numbers! When hammerheads do mate, everything happens
internally. A recently observed behavior in captive bonnetheads also seems to indicate that
hammerheads may be the first cartilaginous fish to show parthenogenesis or reproduction without
fertilization.
This is kind of cool because this actually means that asexual reproduction has been
observed in all major jaw vertebrate lineages except mammals (unless you count
Jesus). Fertilized by a father or not, the young will develop inside the mother’s body
and after about 9 months she’ll give birth to anywhere from 10 to 50 live baby sharks – also
called “pups.” They’re on their own after that, however, because Mom and Dad don’t
take any part in raising them. Hammerheads have been observed to have
an average lifespan of around 25 to 30 years but depending on the species
may be able to live even longer. The size of hammerhead sharks varies pretty
drastically between the species. They can grow anywhere from 3 feet (1 meter) all the way up to
20 feet (6 meters).
The largest hammerhead sharks, the great hammerheads, can weight up to 1,000
pounds (454 kg) but smaller species may weigh as little as 6 pounds (2.7 kg). They appear grey/blue
and sometimes even olive colored along their back while their undersides are a lighter color to
help with camouflage against the bright light shining through the surf. They can even get a tan
from the sun’s rays as they spend a lot of time near the top of the water column or in more
shallow water. They live worldwide in warm, temperate and tropical waters and,
although they are pretty widespread, some species of hammerheads are endangered
due to hunting. Recently, measures have been taken to try and help reduce the amount
of endangered hammerheads killed per year. In Hawaiian culture, sharks were revered as
gods and it was believed that when a person died she would be able to transform into
a shark that would help protect and defend her living relatives. These sharks
were referred to as the family’s ‘aumakua.’ Even today it’s believed that seeing
a hammerhead in the waters of Maui is a sign of balance in the ocean and
that families are being watched over.
For more information on hammerhead
sharks check out the links in the description. Let us know which animal you
would like to learn about in the comments. Thank you for watching and be sure to give
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