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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