Have you ever dreamt of swimming alongside one of nature’s top predators? While that might sound off putting for many non-divers, most scuba divers would seize the opportunity in a heartbeat.
The ocean is a battlefield of species trying to compete for survival and food. At the bottom of the food chain, animals need to be smart in order to survive, while at the top, they need to be strong and powerful.When it comes powerful predatory fish, few are stronger and tougher than the bull shark – one of the oceans most feared predators.
What is a Bull Shark?
Bull sharks are a member of the requiem shark family, which also include other well-known shark species such as; black tip reef sharks, Galapagos sharks, and the infamous tiger shark. They have different names around the world, like ‘Zambezi Shark’ in Africa, and ‘Lake Nicaragua Shark’ in Nicaragua, however, scientifically they are known as Carcharhinus leucas. They are probably most well known for their ability to leave their salt water homes and travel far up rivers. Because of this, some people call them river sharks, although they shouldn’t be confused with the genus Glyphis, which contains true freshwater sharks.
How to Identify a Bull Shark?
As the name implies, bull sharks have remarkably bullish features. They are large and are much stockier than other requiem sharks of a similar length. The male is slightly smaller than the female, who have an average length of 2.4 metres and an average weight of 130kg. Apart from their size, they also have a much shorter and broader snout than most of their requiem cousins.
What was the Biggest Bull Shark?
Although 2.4 metres and 130kg is the average size of a female bull shark, much larger specimens of up to 3.5 metres are commonly reported. The largest accurately measured bull shark was caught in a river in South Africa. It was a pregnant female which measured four metres long and had an estimated weight of between 400 and 500 kilograms. She was named Nyami Nyami – after the Zambezi river God – and was tagged shortly before being released and monitored by scientists.
Where can I find Bull Sharks?
Bull sharks can be found throughout most of the world’s tropical and subtropical seas. In the Atlantic, they can be found from the Massachusetts coastline, all the way down to southern Brazil, and much of western Africa. The Indian ocean population spreads from South Africa to Kenya and Madagascar, and again from India all the way to the Philippines. The only place you don’t find them in Australia is along the southern coastline, and they can be seen throughout many of the Pacific archipelagos.
Bull Shark Habitats
They can be found living to a maximum depth of 150 metres, however sightings below 40 metres are rare, and they tend to prefer living in shallow water, where the reduced visibility aids them with hunting.
There are significant populations of bull sharks in several major rivers around the world – there more than 500 bull sharks living in the Brisbane river. They have been found in some very unusual locations, such as; Baghdad in Iraq, Illinois in USA, and bull sharks have even travelled 4,000 kilometres up the Amazon River to Iquitos in Peru.
How can Bull Sharks Live in Freshwater?
Bull sharks are what scientists call “diadromous”. This means they can easily swim between fresh water and salt water. Bull sharks are not only able to transfer between salt water to fresh water; they are also “euryhaline fish” which means they can adapt their bodies to live in water with higher or lower salinity than normal seawater, such as brackish waters and estuaries.
All fish are able to live in their environment because of a process known as osmoregulation, which is where an organism is able to maintain a constant level of body water concentration. Because of this, most saltwater fish cannot enter freshwater for an extended period of time, and vice-versa for freshwater fish. Doing so could result in death.
Bull sharks are different. They have evolved a special method of osmoregulation, with their kidneys producing large amounts of dilute urine to help recycle salt, and their gills are likely to help absorb any sodium and chloride from surrounding freshwater. They also have a specialised gland – known as the rectal gland- near their tails that allows them to control the amount of salt in their body, although this gland weakens over their life, so the majority of bull sharks found in fresh water are younger, while the older sharks tend to prefer saltwater.
The reason bull sharks can pass freely between saltwater and freshwater is purely for reproductive purposes. The open ocean can be a very dangerous place – especially for a baby bull shark less than one metre in length. The baby bull sharks are born in fresh and brackish water so that other, much larger ocean going predators cannot get to them. The new born bull sharks could actually spend their entire lives in freshwater, although they tend not to because mating opportunities and a constant supply of food are scarce.
Best Place to Dive with Bull Sharks
While it is true that bull sharks can be found throughout most of the world’s tropical and subtropical oceans, scuba diving with them is less common than you might think.
Probably the world’s best location for diving with bull sharks is Pacific Harbour in Fiji, where on occasion, more than 70 bull sharks can be spotted on a single dive. It is not only bull sharks you will find here either. On a single dive, it is possible to see tawny nurse, grey reef, black and white tips, and even the occasional tiger shark.
Another bull shark hotspot is in Playa del Carmen, Mexico. The best time to find them here is between November and March, as they spend some time there before migrating north. It also happens to be when the waters are warm and at their clearest.
Bull Shark Attacks on Humans?
While bull sharks are named so for their appearance, a small part of that name comes from their temperament. They are considered to be the third most dangerous shark species to humans after great white sharks and tiger sharks, and they tend to be found in places where humans like to hang out.
While this might seem like a good idea NOT to dive with bull sharks, you shouldn’t worry about one popping up on your favourite dive site. The vast majority of bull shark incidents take place is shallow, murky waters, such as up rivers, in harbours, and shallow surfing waters.
Because of the bull sharks unusual ability to travel far up river, bull sharks come into more contact with humans than any other shark species, yet attacks are still relatively rare. The majority of reported incidents involve fishermen standing in the shallows, river bathers, or surfers. The handful of incidents involving divers usually also involve a spear gun…
Bull Shark Facts
1.Bull sharks have the strongest bite of all sharks, with a bite force of 5,914 pounds.
2. Bull sharks give birth to live young, and the new born bull sharks can measure as much as 81cm.
3. Bull sharks can be found in some strange places, but probably the strangest is a golf course lake in Queensland, Australia. Back in 2011, heavy rains flooded a golf course and somehow eight bull sharks made their way into one of the lakes.
4. Although the bull shark pups are safer in fresh water than salt water, they still need to be careful as much larger crocodiles could still easily make a meal of one. If threatened, they can vomit to try and confuse any attackers while they try to get away.
5. In the wild, they can live for up to 25 years! However, those that try to spend their lives in freshwater rarely make it to five years old.
If you are ready to experience the thrill of a lifetime, follow us to find the best places to dive with bull sharks in Fiji and Playa del Carmen, Mexico. For those who are really seeking adventure, Playa del Carmen is also very close to the famous Mexican Cenote cave systems, so you can double up on your fix of adrenaline.
Have you been diving with these impressive predators before? If so, we would love to hear about it! Let us know how you encounters went in the comments below.
‘Diving with Bull Sharks’ was written by Mike