The Bull Shark – They’re everywhere you wouldn’t expect them to be! Known as the Carcharhinus Leucas in the scientific community, it has a stocky figure and a broad, flat snout. This is one of 43 shark species that can live in both seawater and freshwater. That fact alone makes this one of the best known shark species. This species is known by several different names depending on its whereabouts: Zambezi Shark, Nicaragua Shark, or Ganges River Shark.
But this shark is also known as one of the top 3 sharks most likely to attack humans (the other 2 are the Great White Shark and the Tiger Shark). Of course, we know that shark attacks are extremely rare (less than 4.5 deaths by shark attacks per year globally), but nonetheless, this shark has been nicknamed “The Pit Bull of the Sea” because if its aggressive behavior.
Most sharks have the same salt concentration in the blood as the sea water they are swimming in. This isn’t the case with Bull Sharks. Instead, they only have 50% of the salt concentration in their blood. This makes them very special as they are able to switch from saltwater to freshwater very easily. The only consequence is they produce 20 times more urine when swimming in fresh water.
After about 10 years, they reach maturity. Adults are normally about 3.5 meters (11 feet) long and weigh approximately 300 kilograms (660 pounds). Typically, females are larger than makes and generally live longer. Most males live for about 13 years, while females live to about 17 years of age.
These special hunters are migrants. They are found in many various areas including Oceans, rivers, and even some fresh water lakes! They tend to stay in warm and moderately deep waters around 30 to 150 meters (150 to 500ft) deep.
It seems the Bull Shark favors the Atlantic, Indian, and Pacific Oceans. Some of their favorite rivers include the Brisbane River, Amazon River, Ganges River, Barhamputra River, Potomac River and the Mississippi River. They have been spotted several hundred miles upstream in these rivers, but typically stay within 100 miles of the Ocean. No attacks on humans have ever been recorded in these rivers.
They are in fresh water lakes, too! It’s not too uncommon to see them in Lake Nicaragua and Lake Ponchartrain, just to name a couple. But if there is easy access from a river and the lake is deep enough (about 30 meters or 150 feet), they’ll check it out and maybe even make themselves at home for a while.
This is one of the more social species and sometimes even hunt in groups. There is still quite a bit of mystery surrounding their social structure, but it seems females tend to have dominance over males.
The Bull Shark is known to eat almost anything. The preferred prey includes bony fish, small sharks, turtles, birds, and some species of dolphins.
These sharks are Viviparous, which means pup sharks develop in the womb of its mother, similar to humans. Typically, the pregnancy period is about 1 year, usually during the summer months but sometimes in early autumn as well. Pups are about 60cm (24in) and mothers give birth to 5 to 15 pups at once.
Interactions with Humans
While the Bull Shark is one of just 3 shark species to attack humans unprovoked, attacks are extremely rare. Especially when you consider that thousands of people wash their bodies daily in the Ganges River for religious purposes. This just so happens to be a preferred area for the shark.
This species is not hunted much by humans. The biggest human threat to these creatures are getting caught in fish nets.
Five Fun Facts About Bull Sharks
Bull sharks are so named because their thick, stout body and short, blunt snout give them the appearance of a bull. They’re also rather aggressive and bull-headed, and they like to bully their prey with head butts before they eat it.
Bull Sharks are medium-sized sharks that can grow up to 11 feet long and weigh about 700 pounds, although females generally top out at 5 feet and males usually reach 7 feet in length. They’re gray on top and white on bottom so that they’re camouflaged against the dark depths when prey is above them, and they blend in to the lighter surface when prey is below them.
Bull Sharks are pretty fascinating creatures, as you’re about to see:
1. Bull Sharks have lots and lots of teeth
All sharks have jaws that are filled with sharp, serrated teeth. The teeth are in rows that act like conveyor belts. When one tooth is lost, the tooth behind it moves forward, sometimes as quickly as within a day, to replace the lost one. A shark may lose and re-grow more than 20,000 teeth over the course of its lifetime!
The average number of rows of teeth in a shark’s jaw is 15, but the Bull Shark isn’t your average shark. It’s certainly not a bull you want to run with: The Bull Shark has around 50 rows of teeth in its jaws, and each row has about 7 teeth, for a grand total of around 350 teeth in its mouth at any given time.
2. Bull sharks enjoy fresh water as much as salt water
Sharks have to have salt in their body for survival. When excess accumulations of salt build up in the body, a rectal gland excretes the excess. The rectal gland of the Bull Shark is less active than that of other sharks, which makes them able to live in fresh water. When their body needs more salt, the liver gets to work producing urea, which allows them to adapt to any change in salinity.
Bull Sharks have been known to inhabit rivers and freshwater lakes. In fact, a Bull Shark was spotted in Illinois after swimming up the Mississippi River, and another swam 2,000 miles up the Amazon River in Peru.
In Queensland, Australia, there’s a golf course with a large freshwater lake that’s home to a school of Bull Sharks who were trapped there after a flood in the ’90s. The golf course is popular among local golfers for the monthly tournament called the “Shark Lake Challenge.”
3. Bull Sharks give birth to live young
Sharks give birth in one of three ways. If they’re oviparous, they lay a sac full of eggs (called a “mermaid’s purse”), which attaches itself to a rock or other surface until the eggs are ready to hatch. If they’re viviparous, they gestate live shark pups and then give birth to them live. If they’re ovoviviparous, they develop eggs, which hatch in the womb. The newly hatched sharks are birthed live.
Bull Sharks are viviparous, and a female shark will have between four and 10 sharks per litter. The gestation period for Bull Sharks is 12 months, after which they give birth in fresh water because the pups are born with a low tolerance for salinity. Bull Shark pups are about two feet long when they’re born, and once they develop a little, they swim out to sea.
Bull Sharks have a lifespan of about 12 years in the wild.
4. Bull Sharks are considered by many experts to be the most dangerous shark
Tiger sharks and great white sharks join the Bull Shark as the Trinity of Terror, the three sharks identified as the most frequent attackers of humans. In fact, the Bull Shark was likely responsible for the 1919 attacks that inspired the movie Jaws, which increased the number of cases of severe galeophobia, or the fear of sharks, from a handful to a nation full.
Bull Sharks like warm waters near the shore, much like humans. They’re common, and aggressive, also like humans, and they’re agile and pretty fast, reaching speeds of up to 12 miles per hour. But much like the great white shark, Bull Sharks rarely actually eat humans, but rather bump ‘n’ bite ’em out of curiosity. Once they get a nibble, they roll their eyes in indignation and swim off to find something edible. (The tiger shark, on the other hand, will eat just about anything.)
Unfortunately for those humans who are “tasted,” the Bull Shark has the highest bite force among all sharks, so that little nibble comes at a force of 1,300 pounds per foot.
5. But humans are more dangerous to the Bull Shark than the Bull Shark is to humans
Bull Sharks are classified as “near endangered” on the IUCN’s Red List. Although Bull Sharks are very commonly seen by humans due to their habitat, their numbers are dwindling due to over-fishing of sharks in general, and particularly sharks that are easy to catch or trap, such as those that live in shallow waters near shore.
Bull Sharks and other species are killed for their fins, liver oils, and skin. The fins are used for the Asian delicacy shark fin soup, and the liver oil finds its way into cosmetics and vitamins. The skin is used for accessories like sharkskin belts and boots. But is a bowl of fin soup or a smooth lipstick worth devastating entire shark species? Some seem to think so.
But the fact is, scientists very recently estimated that humans kill an astonishing 100 to 273 million sharks every year. If we split the change and call it 200 million sharks, that adds up to 380 sharks killed every minute of every day. In the time it takes you to say the word “shark!” six sharks have been killed.
Compare those numbers to the 16 people who are attacked by sharks every year and the one person who dies from a shark attack every two years, and it’s easy to see who’s really the most dangerous predator in the ocean.
I am broadly interested in how human activities influence the ability of wildlife to persist in the modified environments that we create.
Specifically, my research investigates how the configuration and composition of landscapes influence the movement and population dynamics of forest birds. Both natural and human-derived fragmenting of habitat can influence where birds settle, how they access the resources they need to survive and reproduce, and these factors in turn affect population demographics. Most recently, I have been studying the ability of individuals to move through and utilize forested areas which have been modified through timber harvest as they seek out resources for the breeding and postfledging phases. As well I am working in collaboration with Parks Canada scientists to examine in the influence of high density moose populations on forest bird communities in Gros Morne National Park. Many of my projects are conducted in collaboration or consultation with representatives of industry and government agencies, seeking to improve the management and sustainability of natural resource extraction.