Eel-usive Tuna: Siobhan Nuri on the Crisis Facing Our Eels
At the Endangered Species National Hui, freshwater fisheries scientist and University of Waikato PhD candidate Siobhan Nuri took the audience on a journey through the lives of one of our most remarkable but declining freshwater taonga: tuna - native eels.
Longfin and shortfin eels are endemic to Aotearoa and New Zealand's top freshwater predator, playing a critical role in the health of our awa. But they are increasingly under pressure. Nationally, 76% of native freshwater fish are now threatened with, or at risk of extinction.
Siobhan explained that for tuna, the threats are compounding. Habitat loss, migration barriers such as dams, the loss of vegetation, and water pollution are all putting pressure on a species with an extraordinary yet still largely elusive life cycle.
Siobhan's research addresses a significant gap in our understanding of that life cycle: their earliest life stages. Her fieldwork focuses on how longfin and shortfin tuna return from their ocean spawning grounds as glass eels and transition into freshwater ecosystems.
Working at river mouths and key catchments, she is building a clearer picture of migration timing, pathways, and the environmental factors shaping tuna survival at this critical stage.
Siobhan guided attendees through the journey tuna undertake between freshwater and the ocean, including a crash course in stable isotopes to stories of the species' epic migrations. Female longfin eels can live to 100 years old, spending most of that lifetime in our rivers and lakes before making one final journey to their spawning grounds in the Pacific.
Climate change adds further uncertainty. Changes to ocean currents could affect these migrations, but the full extent of the impact remains unknown.
The solutions, Siobhan explained, are within reach: habitat restoration, riparian planting, education, and ongoing monitoring. Siobhan has also been taking her research into the classroom, incorporating the tuna lifecycle into the curriculum at kura to help build understanding of this taonga and inspire the next generation of kaitiaki.
One key message stood out: leave the big ones. The largest tuna are the breeders, the ones that will make the long journey back to Tonga to reproduce, and their survival is critical to the future of the species. Healthy eels mean healthy water, and protecting tuna means protecting the freshwater ecosystems we all depend on.
Ngā mihi Siobhan, for sharing your mātauranga 💙.
You can support the restoration of our waterways and help educate others about our native freshwater species by adopting a stream near you through our Awhi Awa | Embrace A Stream initiative:
