Take an incredible journey with a great white shark and see the dangers she faces on the way. Based on real science, we see remarkable encounters with other marine species
Creative learning activities, incredible facts and information for their conservation. Ideal inspiration for teaching ocean themed topics .
Sharks are just one part of the elasmobranchs - these fish all have a cartilaginous skeleton. This simply means their bones are flexible and as such, offer additional flexibility.
The rays and primitive chimeras (e.g. the spotted ratfish) are related to the sharks, although there are key features that make them distinct...
Despite having a diverse range of shapes and sizes, the sharks all have a similar body plan.
The cartilaginous skeleton means the fins are far more rigid than other fish. The shape of their fins tells you a great deal about the lifestyle of the shark (see the Shark Skool "Fin-tastic Fins" activity).
The differences in their physical features allows scientists to further split the "shark family" in to orders...
Shark reproduction is very bizarre and not only do sharks have three utterly different approaches to having young, the number of offspring, known as pups, varies wildly between species.
As the table demonstrates, the litter sizes range from a handful to hundreds!
All sharks share a method of internal fertilization, with the male using modified pelvic fins (claspers) when mating.
One aspect to consider with shark reproduction is that often sharks take, relative to other fish, a very long time to reach maturity and, whilst there are some large litters, populations take a long time to recover from overfishing or other pressures.
Oviparity is seen in some species with the female laying eggs outside of her body. These have a leathery egg case (often seen on beaches washed up - known as "mermaid's purses").
Sometimes these eggs have strands that tangle in the seabed vegetation, in other cases, the egg is wedged in crevices (they may have projections that help secure the egg in place.
Just like any egg, the embryo relies on a yolk sac to nourish the pup until it is big enough to emerge.
Another method is employed by ovoviviparous species; instead of leaving the eggs to grow and face the dangers of the outside world, the female sharks retain the eggs inside their body.
Not all the eggs grow and these are eaten by the developing young inside the uterus (this is called "oophagy").
In some cases, the young may even devour their siblings - known as inter-uterine cannibalism.
This strategy allows the young to be born at a greater size and potentially have a greater chance of survival.
Viviparous species of shark also grow their pups within the female, but rather then feeding on eggs or siblings, they are linked to their mother's blood system through a special organ called a placenta. The placenta (just like in humans) carries oxygen and nutrients via an umbilical cord which is sited low on their abdomen, between the pelvic fins.
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