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26 Mar 2019

A slippery journey to New Caledonia

A once in a lifetime trip to New Caledonia is on many bucket lists, but the eels of Centennial Parklands walk the walk and will soon embark on an incredible journey.

Autumn is traditionally a quiet time in nature following the hectic breeding season during spring and summer, but for the long-finned eel (Anguilla reinhardtii) it's time for one of life’s biggest adventures – a cross-country trip followed by a trans-Pacific swim.

Commonly misinterpreted as snakes, pests or menacing creatures from the deep, these native fish inhabit most of Centennial Park’s ponds and can often be seen gliding along just under the surface looking for food.

They are predominately carnivorous, feeding on insects, small fish and even young birds. They are not aggressive, and contrary to most perceptions, they have very short, platelike teeth which are of little threat to humans.

Catch Me If You Dare

Long-finned eels get their name from their top fin covering almost half the length of their body and can live for up to 100 years.

Waterway warriors

These native eels play a very important role in the Parkland's pond ecosystem. They help control introduced European carp numbers by eating young fish before they reach breeding age, and assist in keeping bird populations at a sustainable level.

A little known fact about eels is the incredible journey they undertake to breed. During autumn, when there is increased rainfall along Australia’s east coast, mature eels migrate to the sea and swim to their spawning grounds – in New Caledonia!

centennial park eels
Mythbusters beware, these eels do migrate to great lengths.

Finding love

Long-finned eels only breed once in their lives and it is the last thing that they will do before they die. The age range to reach sexual maturity can be anything from 20 – 80 years.

In Centennial Park, adult eels make their way from the ponds down to Botany Bay, sometimes using stormwater drains that link the ponds, but at times actually leaving the water to slide and wriggle overland to close bodies of water.

Here they are compelled by instinct and nature to journey to the warm waters of the Pacific to find love the old fashioned way.

The spawning takes place in extremely deep tropical water in an ocean trench, which can be up to 10 kilometres deep and is found at the edge of the ocean shelf surrounding New Caledonia.

Born into salt water, the eggs hatch and are left to fend for themselves. The female eel can produce around 20 million eggs and it's safe to say that  most of the eels found in the Parklands are primarily born in New Caledonia. 

It's not all fun and games though, after spawning the adult dies and for every million eggs produced, only one will live long enough to make it as a mature adult. 

eel elver, centennial park
The next generation of eels make their way to Sydney.

A tricky transformation

Once hatched, the eel larvae (Leptocephali), which looks a bit like a see through gum leaf, use the Pacific Ocean currents to drift its way across the ocean towards the east coast of Australia. By this stage the eels have grown from this flat leafy shape into a more eel like creature called a glass eel.

Eels make their way to Centennial Parklands ponds by entering the waters of Botany Bay. Once in Botany Bay, the glass eels stop feeding as they move into the inlet, near Sydney Airport, where fresh water meets salt water.

In the fresh water, the eels body will change colour (the see-through camouflage is no longer needed) and the glass eel becomes an Elver. As an Elver, they are ready to make their journey towards the ponds of the Parklands.

The Elvers most likely make use of the green corridor between the Parklands and Botany Bay; the corridor consists of the Botany Wetlands, ponds in Eastlakes and the ponds at the Australian Golf Courses.

From there, the journey continues along the man-made stormwater channels and around Randwick Racecourse till they reach the inlets of the Parklands’ Musgrave and Kensington ponds. 

The maturing of an Elver to an adult eel can take a number of years. The Parklands ponds are a safe environment for the eels to grow and develop as there is an abundance of food for them, with plenty of prey such as juvenile waterfowl, water invertebrates, small carp and other fish to feed on.

eel centennial park
A variety of natural camouflage techniques are used throughout the journey. 
 

The cycle continues

Once they an eel reaches maturity, it will embark on the 2,000 kilometre epic journey to return to their place of birth, returning to New Caledonia.

The eel knows its time to make this journey when they no longer need to eat. The female will also become heavy with eggs, the male with milt (semen).

Even with all of the changes in the landscape since they travelled the path as an Elver, they can still manage to find their way back to the bay. As they near the bay and the smell of salt is in the water they adjust their gills to this once familiar water.

The life cycle of the long-fined eel continues with the death of the adult eel and the eel larvae drifting through the Pacific currents towards Australia.

Hear from Sam Crosby below on a recent documentary about the migration. 

Category: History, Nature

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