Bull Shark

© David Fleetham / gettyimages.com

The bull shark (Carcharhinus leucas),  are also known as the "Zambezi shark" or "Zambi" in Africa (check out the research being done by Meaghen McCord and the South African Shark Conservancy on these animals) and Nicaragua shark in Nicaragua.

Robust-bodied and having a blunt, rounded snout, these are solid animals and are easily bulls of the ocean. The name also comes from them head-butting their prey. The first dorsal fin is large and broadly triangular; the second dorsal fin is very small. Their pectoral fins are large and angular, and are usually a dark gray, fading to white on their sides. Lets learn a little bit more about them...

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© E. R. Degginger/ AA / Animals Animals

These sharks don’t get as big as others (the largest being recorded at 3.5 m/11.5 ft), but they’re hefty in weight (over 230 kg/500 lbs)! Dr. Neil Hammerschlag, research assistant professor at University of Miami, the director of the R. J. Dunlap Marine Conservation Program and his team pulled up a 1,000 lb giant up back in 2012. Found in tropical to subtropical coastal waters, as well as estuaries, these sharks can tolerate a wide range of salinity (e.g. freshwater, brackish and marine). These sharks can be found in bays, harbors, lagoons and river mouths. #Finfact: Bull sharks have been found up the Mississippi! Bull sharks have also been found very well into the Amazon River, and in Nicaragua been seen leaping into rapids to reach inland Lake Nicaragua.

​Although many people think rays and sharks are solely saltwater animals, quite a few are found to frequent freshwater habitats (we'll be talking about these sharks with researcher Jonathan Davis soon). #Finfact: There are more than 30 species of shark or ray that spend some or all of their time in fresh water. It isn’t completely known why these animals developed freshwater tolerance, but one theory is that bull sharks needed a competitive edge for resources found in both freshwater/salt water (e.g. habitat, food).

*ADVANCED SCIENCE SECTION ALERT*
Ichthyologist Thomas Thorson studied bull sharks of Lake Nicaragua and discovered that these sharks regularly swam the Rio San Juan that connects Lake Nicaragua to the Caribbean Sea (remember the pink bull shark image). In this report, Thorson and his colleagues tested blood/body fluids of bull sharks for internal concentration of solutes (sodium, chloride, urea and TMAO). What they found was a loss of osmotic pressure due to a reduction of sodium, chloride and urea. 

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© Adrian Hepworth / www.photoshot.com

So THAT’S the secret. These animals adapt to freshwater by reducing concentration gradients! Neat, huh? We're not experts on this topic, so here's a nice little infographic that touches on the subject if the above didn't make sense.

You may know that bull sharks have the third highest unprovoked human attacks. According to Florida Museum of Natural History, there have been 67 non-fatal unprovoked attacks since 1580, with 26 proving fatal and 93 in total. This video is one of the more famous bull shark 'attacks,' mainly because it was televised. 

The theory of these sharks having the highest testosterone in the animal kingdom has been debated, but the science does show that one male bull shark had a circulating testosterone level of 358 ng/ml. The other male had a meager 2.7 ng/ml. Other sharks have also shown high levels- Sphyrna tiburo had levels in the 300-400 ng/ml range. 

Teleosts and small sharks make up the vast majority of the bull shark diet. Other food items include sea turtles, dolphins, crabs, shrimp, sea birds and squid. Due to their large size, occurrence in fresh water, variety of prey and being known as aggressive, these sharks should be treated with respect and caution.

Bull sharks are labeled by the IUCN as Near Threatened (NT). They are known to be caught in long-lines and for finning purposes. They are also a popular sport fish in fishing tournaments, due to their large size and putting up quite the fight. 

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​what are your thoughts on bull sharks?

glossary

• Cosmopolitan: Worldwide distribution.
• Dorsal fin: Fin located on the back.
• Fecundity: The natural capability to produce offspring. 
• Gestation: The period in which a fetus develops, beginning with fertilization and ends at birth.
• IUCN: International Union for Conservation of Nature.
• Teleost: Bony fishes.
• Testosterone: A hormone produced by the testicles and is responsible for the proper development of male sexual characteristics. 
• Oophagy: Sometimes called "oviphagy;" when developing embryos feed on unfertilized eggs.
• Pectoral fins: Fins located behind the gills on either side.
• Pup: Give birth to baby sharks (pups).
• Pups: Baby sharks.
• Viviparous: Eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark between the pectoral fins).​

say hello!

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