New Zealand and the Chatham Islands have two main species of eel (tuna), the endemic longfin and the shortfin eel (shared with Australia), so named for the length of their fins. A third eels species the Australian longfin or speckled eel is also found occasionally in the upper half of the North island. Eels have long been a traditional and sustainable food for many New Zealanders. However longfin eels are now considered threatened, and shortfins are far less abundant than they used to be, in many parts of the country. The eels we all know so well have a life story which is quite startling.
An Amazing Journey
Longfin eels start their lives as eggs, most likely laid in deep sea trenches in the Pacific Ocean near Tonga. After hatching, the clear, leaf like larvae, they drift at sea for almost a year. They eat plankton and are themselves eaten by larger marine creatures during long journey here. As they near our coasts they turn into tiny glass eels which find their way to fresh water streams and rivers where they grow into small grey-brown eels, called elvers.
For the next 10 to 80 years they grow and live in our streams, lakes, drains and wetlands. Once mature (on average around 20 years for shortfin females and 20 to well over 40 years for longfin) eels develop the urge to breed. In autumn for shortfins and both autumn and spring for longfins and mostly during high rain events, the adult eels return to the sea and spend the next five months travelling 2500 kilometres back to the deep sea trenches near Tonga. Once there female eels lay millions of eggs (the larger the eel the more eggs a females carries), which the males then fertilise. This is the one and only time the eels breed, then they will die.
The tiny eels which make their homes in our bodies of fresh water, take a hazardous, amazing journey and arrive here with the help of sea currents. They depend on a healthy population both in the Chatham's and New Zealand to sustain this precarious life cycle.
If you have any stories to share about our local eels the Board would be very grateful to hear them
Chatham Islands Conservation Board