Amazon River Bull Shark Facts
| Wildlife & Flora
It may surprise you to learn that there are sharks lurking in the murky waters of the Amazon River. And not just any shark for that matter. The Amazon region is home to what scientists consider to be the most dangerous shark in the world – the mighty bull shark. Here’s everything you could want to know about these fearsome creatures, including an answer to the puzzle of why they are found in the river in the first place.
The bull shark (scientific name: carcharhinus leucas) is named after the fierce land animal and acquired this label for a couple of reasons. First, it has a stocky shape and a short, blunt snout. Second, bull sharks are notorious for their aggressive, unpredictable behaviour and known to head-butt their prey in a bullish fashion as a prelude to attacking. These sharks are also thought to dislike bright colours, with a tendency to launch at brightly coloured nets more than neutral coloured ones.
Bull sharks are hefty, heavily built animals, spanning lengths of around 7 feet and with an average weight of 500 pounds. However, there are reports of bull sharks reaching a staggering 13 feet, though these remain unconfirmed. Females are larger and longer-living than males and they are also thought to be the dominant sex in the shark’s social hierarchy.
Bull sharks belong to the family of requiem sharks, along with their equally fearsome cousins, tiger and white sharks. They are grey on top with a white underbelly and have long pectoral fins with dark tips. Bull sharks possess a remarkable set of teeth encompassing hundreds of razor-sharp, heavily serrated teeth which are located in rotatable rows. They also have the strongest bite force of any shark, of up to 1,300 pounds.
Bull sharks are relatively common and found worldwide in warm, shallow waters along coasts and in estuaries, rivers and tributaries. Perhaps the most intriguing characteristic of the bull shark is the fact its habitat extends to brackish and freshwater environments. In fact, it is virtually unique amongst sharks in its ability to adapt to both salt and freshwater conditions. This is due to the unique “osmoregulating” functioning of their kidneys which detect changes in water salinity and inhibit the excretion of vital salts which are instead recycled in the shark’s body enabling it to maintain sufficient salt levels in its blood.
There’s also another reason behind this freshwater adaptation. Unlike most sharks, bull sharks don’t lay eggs or rear their young. Instead, pups are born live, just as with mammals, and already span two feet long at birth. Females will seek freshwater environments to give birth as this provides their young with a better chance of survival (shallow waters contain les predators) as well as allowing them to build up sufficient tolerance to saltier water conditions over time.
Whilst bull sharks spend most of their time in shallow ocean waters bordering tropical shorelines, they are therefore known to venture well inland. In the Amazon, they migrate up and down the river seasonally and have been reported as far upstream as Iquitos in Peru – some 4,000 km from the shore. Due to its proximity to the ocean, bull sharks can be most frequently sighted in the lower reaches of the Brazilian Amazon.
DIET AND HUNTING BEHAVIOUR
Bull sharks are not fussy and will eat just about anything they can sink their teeth into. Large, fast and vicious, they are apex predators, meaning that nothing habitually preys on them. However, there have been occasional reports of attacks on bull sharks by saltwater crocodiles and even by members of their own species who may prey on smaller individuals.
Their diet mainly centres around other fish, stingray, turtles, birds and crustaceans. However, they are opportunistic hunters and given the chance, their powerful jaws enable them to feast on a whole range of larger animals. These include dolphins, other sharks, land mammals like sloths, pigs and dogs that come to the water’s edge.
BULL SHARKS AND HUMANS
Bulls sharks are reputedly the deadliest shark in the world. This is due to their physical strength and aggression, combined with their preference for shallow coastal waters where they are more likely to come into contact with people.
Bull sharks are not endangered, as many species of shark are. However, they are still habitually hunted for their fins, hide, meat and liver oil, which is causing a gradual decline in their numbers. They may also be caught for sport or captured for display in aquariums. Habitat destruction and water pollution may also be contributing negatively to the health and numbers of these sharks.