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.
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