Sharks in the Amazon?

By Mike Collis

Sharks live in the sea don't they? We know that when the first Spanish explorers came here and saw the mighty Amazon they called it "The Great Inland Sea", but sharks live in salt water and the Amazon is big, but full of fresh water. So are there sharks in the Amazon? The answer is yes.

The Bull shark (Carcharhinus leucas) can adapt to fresh water, in 1963 a 265lb bull shark was caught near Iquitos and Iquitos is nearly 4,000 klms from the Atlantic Ocean. They are more frequently caught in Brazil due to the proximity to the ocean. Bull sharks can thrive in both saltwater and freshwater because they have developed special osmoregulating kidneys that sense the change in salinity of the water they are in. Their kidneys inhibit the excretion of vital salts and thus recycle them throughout their body. This adaptation allows our toothy friends to move into freshwater almost indefinitely. Bull sharks travel up many rivers some as far up as Kentucky on the Ohio River, USA. Other sightings were on the Brisbane River in Australia, the Zambezi River in Africa. A woman was killed by a Bull shark in 2010, 200 miles up a river in New Jersey ,USA. In 2011 during the Queensland floods in Australia bull sharks were seen cruising the streets of the town of Goodna.

Bull sharks are large and stout, with females being larger than males. Adult female bull sharks average 7.9 ft long and typically weigh 290 lbs, whereas the slightly smaller adult male averages 7.4 ft and 210 lbs. While a maximum size of 11 ft is commonly reported, there is a questionable record of a female specimen of exactly 13 ft. The maximum recorded weight of a bull shark was 690 lbs but may be larger. Bull sharks are wider and heavier than other sharks of comparable length, and are grey on top and white below. The second dorsal fin is smaller than the first. The bull shark's caudal fin is longer and lower than that of the larger sharks, it also has a small snout and it lacks an interdorsal ridge. Bull sharks have a bite force of up to 1,300 lb, the highest among all investigated cartilaginous fishes. Bull shark teeth are triangular, and very sharp. They are located in rows which rotate. The first two rows are used in obtaining prey, the other rows rotate into place as they are needed. As teeth are lost, broken, or worn down, they are replaced by new teeth that rotate into place. Its belly is off-white, its top surface is gray, and the eyes are small. The bull shark is also know as the cub, Ganges, Nicaragua, Swan River Whaler, Zambezi, Shovelnose, Slipway Grey, Square-Nose, and Van Rooyen's Shark.

The bull shark is a solitary hunter but they do sometimes hunt in pairs. They eat fish (including other sharks and rays), turtles, birds, mollusks, crustaceans, and dolphins. It will eat almost anything. The bull shark is one of the most frequent attacker of people, as it swims in very shallow waters where people swim and is a very aggressive shark.

Bull sharks give birth to live baby sharks. Litters of 1 to 13 pups are common after a gestation period of about one year. Pups are about 28 inches long at birth and can swim immediately. A pup's fins have black tips, but these markings fade as they get older. The young take about 10 years to reach maturity. Coastal lagoons, river mouths, and other low-salinity estuaries are common nursery habitats.
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