Unlocking the mysterious marine life of eels Tiny, translucent eels may hold the answers to one of the fish world’s great mysteries. Zen Gregor investigates. Tuna, or freshwater eels, hold a very special place for iwi. Widely valued as both a food source and a taonga, they are a culturally significant mahinga kai species. Their survival, and the protection of the waters they live in, is paramount to many.
layers “The act as a daily diary of an eel’s life
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Dr Eimear Egan
Toby Salmon, mana whenua from Ngāti Awa, is in no doubt about the importance of tuna habitat in the Bay of Plenty’s Rangitāiki River. “This is our cupboard, this river, and if we don’t look after it, if we don’t nurture it, we’re going to lose it,” says Salmon. Tuna have a very unusual life cycle that sees them travelling between freshwater and ocean environments, and much remains secret about the mysterious marine phase of their lives.
We know mature adults leave New Zealand’s rivers and swim out to spawn in the western Pacific Ocean. We also know that their larvae return to New Zealand’s coast, transforming into tiny glass eels (named for their translucent appearance) for the start of their freshwater life. No one knows, however, where those spawning grounds are, which ocean currents the larvae use to return or whether shortfin and longfin eels use different ocean spawning grounds and currents. Freshwater fish ecologist Dr Eimear Egan is leading an MBIE-funded Smart Idea project which aims to unlock some of the answers. Over recent months, Egan and her team have been working with mana whenua at three river mouth sites. The chosen rivers are the Rangitāiki, Grey and the
Fresh from their puzzling ocean journey, glass eels – under 7cm in length – congregate in river mouths during spring tides. They soon lose their translucent appearance and continue upstream as elvers. (Lana Young)
20 Water & Atmosphere
February 2020
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