Thursday, May 18, 2017

Tuna report

Hi this is my report about New Zealsnd tuna
Opening statement: There are two main types of eels or tuna in New Zealand- The longfin and the shortfin eel. There are only 16 freshwater eels around the world.  Longfin eels are one of the largest eels in the world and are the only endemic freshwater eel to New Zealand. There are fewer eels today due to the cause of commercial fishing and the loss of wetlands. The scientific name for eels are Anguilla dieffenbachii.

Tuna come in a variety of different colours but they are usually dark brown, black or grey. Although very rarely they can be fully yellow or partially yellow. Longfin eels have poor eyesight but have other great senses to help them survive. Eels can absorb up to 50% of their oxygen through their skin which can get slimy when they are stressed. They have large mouths with sandpaper like teeth that point inwards. They also have sensors that looks like white spots around their mouth to help them detect any movement in front of them.

Freshwater eels can be found all around New Zealand. They are mainly found in rivers or inland lakes usually well inland from the coast. Eels can be able to climb up waterfalls up to 20 meters high while trying to find a river upstream. Longfin eels can survive in many conditions such as dams and drains and can also swim up underground streams. During daylight the main places to find tuna are in water weeds, tree roots, undercut banks and debris piles. They can also squeeze into small gaps and make holes in the mud. Adult longfin eels like fast flowing water and will be found more upstream. While short fins prefer a slower flow in the water. Short Fins are mostly found in swamps, lakes , streams and rivers near the coast. However both species are often found in the same place.

During summer the female eels body changes as it is reaching maturity. Her eyes will enlarge, Their digestive systems shrinks away, Her big bulging heads become more flatter, their belly goes gold and their  causinback goes brown.It will take many months for the eels to reach their breeding destination. Which is somewhere in the tropical waters near Tonga. Once they reach their breeding grounds a huge mass of eels will twist together to fertilise the eggs. The fertilised eggs will then float up to the surface of the water and grow into a leaf shaped larvae. They will then become apart of ocean plankton and will be carried from the currents to the coast of New Zealand. The larvae will head towards rivers and streams to find a new home. Their flat bodies will change transparent and these are called glass eels. As they grow they will then change into elvers which are the young eels that feed on insects and snails. As they move upstream the elvers are able to climb steep waterfalls. Then they will turn into fully grown eels and continue their life cycle

An eel is a carnivore which means it only eats meats it also likes it’s food being alive when it eats it. Small eels will like to eat insect larvae, worms and water snails. As they grow older they can begin eating fish. They will also be able to eat freshwater crayfish and and even small birds such as ducklings. An eel will usually be seen hunting at night, they don’t hunt by vision but have other strong senses such as smelling to help it hunt for food.

Closing statement: Pollution is also another main reason why the eel habitat is being destroyed. Caused by sewage and effluent from meat works, pulp and paper plants that are being discharged into the rivers causing large quantities of oxygen being removed from the water.