River Amazon breakthrough: Shark discovery 'indicator of river's health'

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Bull shark found 450 miles from the ocean in rare discovery

The Amazon River is the largest river, by discharge volume of water, in the world. Though historically considered the second longest, behind the River Nile, much debate remains about the true length of both rivers. The Amazon is often said to be “at least” 6,575 km (4,086 mi) long, though some estimates have said it could be up to 6,992 km (4,345 mi) long. The Nile, meanwhile, has been reported as being “at least” 6,650 km (4,130 mi) long.

The Amazon River is the largest river, by discharge volume of water, in the world.

Though historically considered the second longest, behind the River Nile, much debate remains about the true length of both rivers.

The Amazon is often said to be “at least” 6,575 km (4,086 mi) long, though some estimates have said it could be up to 6,992 km (4,345 mi) long.

Several factors can affect these measurements, notably the position of the geographical source and the mouth of the river.

Both of them act as a home for hundreds of thousands of different animal species.

More than one-third of all known species in the world live in the Amazon rainforest, with more than 5,000 species of fish living in the Amazon basin — though more are being discovered each year.

Alongside the fish, the river supports crustaceans, mammals, reptiles and birds.

There are currently 5,600 species of known fish living in the Amazon, with approximately 50 new species added to that list each year.

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Bull shark

A bull shark was discovered in the River Amazon – more than 450 miles from the Atlantic Ocean. (Image: Nat Geo)

Piranha

Piranhas are just one of the carnivorous predators in the Amazon. (Image: GETTY)

It is home to the arapaima, one of the largest freshwater fish in the world.

The notorious piranha can be found in significant numbers, congregating in large schools that can attack livestock and even humans — only a few species are known to attack humans, however.

Although more commonly a saltwater predator, bull sharks can survive in freshwater too.

They typically measure between 2.25 metres and 2.5 metres in length, but a maximum size of 3.5 metres is often reported.

Freshwater rivers, however, provide significantly less food for them than saltwater areas — and they have been known to attack small mammals, dolphins and humans.

Arapaima fish.

Arapaima fish are some of the largest freshwater fish on Earth. (Image: GETTY)

Jeremy Wade explored the discovery of one of these predators in his recent National Geographic documentary ‘Unknown Waters with Jeremy Wade’.

He spoke to a local fisherman, who discovered a bull shark on the end of their fishing rod during a trip with his son.

The fisherman told Mr Wade: “I said to my son, ‘brace yourself!’ I knew it was a big fish.

“As I was pulling it in, I looked up and saw its tail.

“I looked over to my son and he said, ‘It’s a shark!’”

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Local Amazon fisherman with a bull shark.

The local fisherman had never seen anything like the bull shark in his life. (Image: Nat Geo)

Living some 450 miles away from the Atlantic Ocean, near the Brazilian city of Santarem, neither the fisherman nor his son had ever seen a bull shark before.

Curious as to why the shark was so far from the ocean, the fisherman decided to have a look inside its stomach.

He recalled: “There was nothing in it, it was starving. Its stomach was bare, like an empty bag.”

Mr Wade added: “Bull sharks have always been rare in the Amazon, which makes them a very sensitive indicator of the river’s health.

“If the river is struggling, bull sharks will be the first to disappear.”

Local Amazonian fisherman

The fisherman revealed the bull shark was starving and had nothing in its stomach. (Image: Nat Geo)

He explained that there have been “patchy reports” of bull sharks in the Amazon throughout history.

They have even been caught as far upstream as Iquitos in Peru, some 4,000 kilometres away from the ocean.

But, Mr Wade added, such reports have dried up in the last half century.

He asked: “Could this be the Amazon’s last bull shark?”

Sharks are opportunistic feeders, with the bull shark being no exception to this.

They usually eat in short bursts, and digest for a much longer period of time in order to avoid starvation when food is scarce.

Bull sharks prefer to hunt in murky waters where it is harder for their prey to see the shark coming, hence parts of the Amazon might suit their hunting style.

Yet, despite the threat of an abundance of predators in the Amazon, it does not always put humans off.

In 2007, Slovenian long-distance swimmer Martin Strel became the first person to swim the entire length of the river, spending up to 10 hours a day in the water for 66 days.

He had escort boats ready to pour blood into the water to distract carnivorous fish such as piranhas.



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