The Truth About
© Nautilus Productions
23 February 2017
SAND TIGER SHARKS:
Learn more about sharks
- Cartilage skeleton
- 5-7 gill slits
- Short ribs possible, never a full rib cage - Fusiform in body
shape generally, some species dorso-ventrally
- 1-2 dorsal fins
- 1 pair pectoral, 1 pair pelvic fins
- Protruding snout with nostrils
- Cresent-shaped mouth
- Spiracle opening in posterior to eyes (evolutionary remnant of bony
fish gill slit, not present in some species) - Dermal denticles in place of
scales like bony fish. - Multiple rows of teeth, up to eight functional rows. The
structure/shape of teeth varies with species and their diets. Replacement teeth
are larger that tooth being replaced. The rate of
tooth replacement varies with species, may be from eight days to a
full year, with the teeth replaced singly or complete row at once.
- Sharks lack the air bladder of bony fish to maintain buoyancy.
Some sharks such as the Sand Tiger are gulpers and surface
periodically to swallow air to assist in buoyancy.
- Large liver,
can occupy as much as 90% of the body cavity or be
25% of the body weight in some species. Adds buoyancy because oils
of liver have lower specific gravity than surrounding water. In
fact, production of liver oils is controlled by the shark to help
compensate for buoyancy changes. Still, sharks are slightly
negative and will sink if they stop swimming.
Like most apex predators the Sand Tiger has a long-gestation
period and large, well-developed young at birth (nearly 3 feet long)
and usually only one or two pups. Reproductive strategy of an apex
predator has many qualities like a human or a mammal: long-gestation;
large, well-developed young at birth; relatively few young born
(millions of eggs for bony fish, fewer than 100 - usually much fewer -
young for sharks).
Most sharks give live birth (young born from oviducts of female instead of
an egg that has been laid) after a long gestation period. The longest
gestation period for any animal is that of the spiny dogfish, Squalus
acanthias, at 22-24 months. It is believed that the male grasps the
females fins with his mouth and uses his two claspers to mate with her.
This violent meeting leaves deep cuts and gashes behind the females head.
These injuries usually heal within a week however. After mating, shark
reproduction occurs in one of three ways:
The male shark has two reproductive organs or "claspers" that
he uses to inseminate the female. The claspers are located between the
two pelvic fins.
- Ovoviviparity-most common. Internal egg laying with gestation
and live birth. Sand tigers have a unique variation of ovoviviparity
called intrauterine cannibalism. The first young in each of a Sand Tiger
two oviducts to reach 60mm tears open its egg and swims to the uterus
where it feeds on its siblings, embryos, and the other unfertilized
eggs for the rest of gestation. Usually two 3 foot long live pups are
born from a mother that is only about 9 feet long. Great whites are also
believed to exhibit intrauterine cannibalism.
- Viviparity-The yolk in the yolk sac is first consumed by embryo,
then uterine milk produced by female is absorbed by an embryo through
the means of a placenta that is formed from the yolk sac to wall of uterus.
Sharks are born live and ready to fend for themselves outside the female.
Viviparous species include the Hammerhead, Bull shark, Blue shark and Lemon sharks.
- Oviparity-An egg case with yolk sac inside for nourishment is laid by
the female on the sea floor or on rocks. "Mermaids purse" is a common
name for swell shark and cat shark egg cases. the Horn sharks egg
cases are screw shaped and are often found wedged tightly into rocks.
Oviparous sharks include the Swell shark and Horn shark.