The Amazing Amazon River Dolphin

The Amazon River Dolphin, (Inia geoffrensis), is also called Bufeo, Boto, and Pink River Dolphin as well as a number of local names. This wonderful dolphin species is confined to freshwaters of the Orinoco, Amazon, and Araguaia/Tocantins River systems. It never moves into seawater and can not move up-river above rapids and shallow water.

 

It is the largest of the river dolphins weighing up to 180 kg and reaching a length of 2.6 m. Most adults are pink, but some have darker backs or are mostly gray. It is believed that the Boto's pink color comes from fine blood vessels close to the surface of the skin.

Amazon River Dolphins are unique in that their neck vertebrae are not fused into a rigid structure. Instead they can bend their neck at a 90 degree angle to their body, and skillfully hunt food in the flooded forest tree roots. They have 25-30 peg-like front teeth for catching prey, mainly  crustaceans, crabs, turtles, and fish.

The Boto's eyes seem small and ineffective but are actually as large as those of other dolphins but are protected by fleshy pads. When the rivers are running fast and filled with muddy water, the Boto’s echolocation allows it to navigate through the flooded forest.

Females become sexually mature between 1.6 - 1.8 m in length when they are between 6 - 10 years old. Females give birth to a single calf every 4-5 years. Mother and offspring stay very close for 2-3 years and the calves are fed milk for the first year. Males appear to reach sexual maturity at body lengths over 2.0 m.

Mythology surrounds the Amazon River Dolphin. It is thought to be a shape shifter, able to change to a young man and seduce village women into pregnancy. In the morning the Encantado (enchanted one) returns to the river as a dolphin.




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WHAT'S SO AMAZING ABOUT SHARK SKIN?

More than four hundred million years ago (Paleozoic Era), long before the existence of bony fishes and before dinosaurs roamed the land; primitive sharks hunted the ancient seas much as they do today. From the Paleozoic Era until now, thousands of marine species have become extinct because they were unable to cope with the slowly changing sea or competition with other animals.

The huge prehistoric shark Megalodon was the most dangerous fish to have ever lived.

Sharks have changed very little over the last 100-200 million years and are as successful today as they were so far in the past. One of their secrets to success is their amazing skin.

 

Dermal denticles

 Believe it or not, the outgrowths from the skin of sharks that form minute scale-like structures are similar to miniature ‘teeth’. It is believed that teeth in the earliest vertebrates arose from these tiny outgrowths.

Shark scales are formed of dentine (like our teeth) and originate from the dermal layer of the skin (bony fish scales originate from the epidermis). The dermal denticles are so hard and so sharp that people have used sharkskin as sandpaper. Japanese sword smiths used shark skin for the hand-grips of swords, making them less likely to slip.

Most denticles point backward so sliding your hand from head to tail feels smooth; sliding your hand in the opposite direction is rough enough to abrade the skin.

Studies have found that the denticles create tiny vortices (whirlpools) behind them. By keeping the water turbulence small and ‘clinging’ to the shark’s surface, drag is reduced and speed is increased. Swimming through the water also generates noise that can warn prey of an approaching predator: the denticles reduce the noise making the shark a deadlier predator.

Most sharks have skin colored to fade into surroundings. Midwater hunters are dark above and pale below. From above a shark looks like the darkness of deep water; from below its belly blends into the sunlight above. Sharks that hunt from ambush on the bottom can have colorful skin that looks like seaweed.

A Great White shark cruises the cool waters of South Australia.

Fins and Tails

The fins of bony fish are supported by extensions of bone that run out into a very thin skin membrane. In sharks the fins are thick and supported by rays (filaments) similar to the keratin in feathers and hair.

The shark’s pectoral fins (equivalent position to our arms) are fairly rigid and designed to provide lift to keep the front of the shark from sinking while swimming.

 Sharks have very distinctive tails (caudal fins). The design of the tail is related to its swimming speed, the amount of lift it needs, and how it catches its prey. Sharks have heterocercal caudal fins which mean the top and bottom lobes are different in shape. The larger upper lobe produces a small amount of lift along with forward motion keeping the tail up and balancing the lift from the pectoral fins.

Like the rest of the shark’s body, the fins are covered in dermal denticles. They reduce drag and noise and increase biological efficiency. Energy saved in swimming is converted to growth and size means safety even for these master predators.

A Basking Shark is a harmless species that preys on plankton by filtering tons of water through its gills.

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THE GREENLAND SHARK; A COLD WATER GIANT

No other shark lives closer to the North Pole than the Greenland Shark (also called Sleeper Shark). This cold water giant is closely related to the Pacific Sleeper Shark and grows to 6.5-7 metres in length and a weight of over 1000 kg. 

Greenland Sharks live in the North Atlantic near Greenland and Iceland where they range into water as deep as 2000 metres. Greenland Sharks are ovoviviparous which means that the eggs hatch inside the female and live pups are born. Scientists believe that it may live to be about 400 years old.

The Greenland Shark (and Sleeper Shark) has the reputation of being very slow and sluggish when caught. Divers report that Greenland sharks are not threatening and are slow swimmers but we may not know the full story of these huge predators. The native Inuit people have legends of sharks attacking their boats.

Examination of Greenland Shark stomachs shows that at times they can be fast and hungry. Contents include squid, fish, polar bears, reindeer, horses, and other Greenland Sharks. William Sommers reports that he has seen Greenland sharks snatching caribou from the water's edge.

It is reported that Greenland Sharks have a problem with parasites (copepods) that attack their eyes. The parasites cause scars that interfere with the shark’s sight. Sharks have a number of senses that detect prey and good eye-sight may not be critical for this species.

The flesh of the Greenland Shark contains a powerful neurotoxin and is poisonous to eat. They seem to be immune to their own poison and are able to eat each other.

Teeth photo are from Canadian Shark Res. Lab.

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The Incredible Octopus

One of the most interesting animals that I have worked with is the octopus. The name is from Greek meaning 8 feet (we call them arms). There are at least 300 species of octopuses and many more are sure to be found. They belong to a larger group of animals that include squid and cuttlefish and are known as cephalopods.

 

At the center of the 8 arms is the mouth with a parrot-like beak used for tearing food apart. In most octopuses the arms are lined along the underside with suction cups that provide a powerful grip.

The bulk of the body is like a rounded sack (mantle) that is quite muscular but has no skeleton. This flexibility allows it to change shape and squeeze through small openings in its rocky home. Inside the mantle are organs for respiration, circulation of blood, and reproduction. Octopuses swim by squeezing water out of the mantle as a form of jet propulsion.

Octopuses have three hearts. Two of these pump blood through the gills to get oxygen from the water and the third heart pumps the blood through the body. Unlike our iron-red blood, an octopus’s blood is blue from the copper that carries the oxygen.

 

Most octopuses don’t live very long breeding just once before they die. Small octopuses like the Blue-ringed live about a year and larger species like the North Pacific Giant may reach as much as 6-7 years old. In all species that have been studied, mating and the hormonal changes associated with it are the cause of death.

Depending on the species, females will lay from a few hundred to many thousands of eggs. After laying the eggs, the female will stop hunting and spend her time guarding her nest. Most eggs hatch within a month or so and the female dies soon after.

 

After hatching, the tiny octopuses are not fully developed and are called larvae. The larvae drift in the surface plankton feeding on small crabs and shrimp-like copepods. When they have developed enough they settle to the bottom and search for a suitable ‘home’. 

 

Many octopuses ‘decorate’ this home with pieces of shell and rock to make it more difficult for predators to see.

 

Octopuses are surprisingly intelligent; probably the most intelligent of all animals without backbones. Their large brain receives information from two very good eyes and millions of sensors all over their body. The complex nervous system allows the octopus to hide from its enemies using incredible camouflage. They can also surprise and confuse an enemy by releasing ink. The ink is a fluid made in their body and containing the pigment melanin (the same dark pigment in human skin).



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