The life cycle of eels

Researcher Erina Watene-Rawiri describes the life cycle of eels.

Updated science: In this video Erina explains that the leptocephali – eel larvae – 'float' back upstream on the current. Current scientific belief is now that the larvae are not passive drifters but have some swimming ability to get them where they need to go. The nature of science is such, that we are often having to reevaluate our ideas and knowledge.

Transcript

ERINA WATENE-RAWIRI
Taonga species are species that are precious to Māori.

Eels are a taonga species, so Māori have relied on eels for generations.

Eels have quite a complex life cycle. They spend part of their life in the ocean and part in freshwater, so if we start with the adults, they’ll be hanging out in the streams and lakes. And then when they’re ready to go out and spawn, they head down stream en masse and out to the ocean. They swim for a couple of thousand miles out towards Tonga where they spawn, at quite a depth.

The eggs then rise to the surface and hatch, and you have these little tiny eel larvae which are see-through and they’re leaf-shaped – they’re called leptocephali. The leptocephali float back to New Zealand on the ocean currents, and just before they head back up into the rivers, they metamorphose into what we call glass eels. Glass eels are tiny see-through baby eels, and they swim up the river, and as they continue on up the river, they change colour, they go black. And they turn into what we call elvers, and elvers are just pretty much miniature versions of adult eels. And they stay in freshwater from anywhere between 20 to 60 to 100 years before they become adults, and then they head back out to sea and spawn again. The adults, when they spawn, they die – only the babies come back.

Acknowledgements:
Erina Watene-Rawiri
Tim & Doug Watts
Glass eel still courtesy of the Vertebrate Zoology Division, YPM ICH.023326, Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA
NZ Eel Processing Co Ltd, Te Kauwhata
The Waikato Tainui College for Research and Development acknowledges the financial support given by the Waikato River Cleanup Trust Fund which is administered by the Waikato River Authority.
The Waikato River Cleanup Trust does not necessarily endorse or support the content of the publication in any way.