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Source: Department of Conservation

World Fish Migration Day celebrates migratory fish and free flowing rivers. Migratory fish species and river connectivity, ki uta ki tai, are important parts of our conservation mahi. This year, we are putting the spotlight on our precious tuna (native eels), and our partnership with Ngāti Apa ki te Rā Tō. 

New Zealand tuna (native eels) are long distance voyagers, migrating from Tonga across the Pacific Ocean and settling in the fresh waters of Aotearoa. Some travel inland all the way to Lake Rotoroa in Nelson Lakes National Park. Here, a special project is monitoring their populations and combining cultural revitalisation with conservation. 

In January, eight Ngāti Apa ki te Rā Tō rangatahi (young people), as well as taiao (environmental) and cultural specialists from Ngāti Apa ki te Rā Tō, teamed up with DOC scientists to undertake a tuna survey and harvest. Together, they experienced first-hand what science can tell us about tuna and discussed the role of Ngāti Apa ki te Rā Tō as kaitiaki of these taonga species and their awa.

Dr Jen Skilton, Pou Taiao (Environmental Manager) at Ngāti Apa ki te Rā Tō and Dr Melissa Griffin, Senior Ranger at DOC reflect on the experience.

Why do you survey tuna populations in Lake Rotoroa?

Jen: As part of the settlement of Ngāti Apa ki te Rā Tō with the Crown, our iwi can harvest tuna from Nelson Lakes for customary purposes. We’ve been taking small numbers of tuna from the lakes since 2012 and it’s really important to us that any harvest doesn’t adversely affect the population.

Part of my role is to investigate the sustainability of this cultural practice and for us as an iwi to learn more about the tuna populations in the lakes. That’s where the monitoring comes in.

DOC freshwater ranger Kate Hunt finishes deploying a fyke net in Lake Rotoroa.

What prompted this project and how did DOC get involed?

Jen: DOC helped us to set up a monitoring programme which included collecting, measuring and weighing tuna. The aim of this was to gain insight into the population structure and the number of tuna in the lake which, as we found out, was quite high!

Melissa: I heard about the harvest when I started in my job in Nelson. I’d heard that iwi put out nets in Lake Rotoroa where the tuna are plentiful. I immediately thought: Wow – free data! When the harvest started, they collected data to ensure it was sustainable. Most tuna being caught are returned to the lake. Now we want to build on that, thinking about climate change and what impact it could have on the tuna.

Ngāti Apa ki te Rā Tō rangatahi and DOC freshwater ranger Suse Harris retrieve a fyke net set along the shore of Lake Rotoroa.

How did you do the survey and what did you find?

Jen: We put out 14 fyke nets at different spots around the lake baited with fishy cat food, which the tuna love! The next morning about 1000 tuna had been captured, with more than 100 in some nets. Some were huge – the biggest was more than 6 kg and 1.5 m long.

Most tuna captured were longfins – we estimate that less than 1% were shortfins. We also found a couple of elvers. It was exciting to find these life stages in the lake, because it’s quite a long way inland. Once we’d weighed and measured the tuna, they were released back into the lake.

Melissa: Handling such large numbers of tuna was a bit tricky. A couple of nets were just writhing with slippery tuna. Here we were, trying to put them all into tubs for processing and the tuna not agreeing with that plan! It was both fun and chaotic. “Oh, there’s an eel out, there’s a tuna out, watch out! there’s a tuna out!” – there were tuna all over the ground!

After a night in the water, this fyke net is writhing with healthy tuna. Smaller fish, like bullies and small tuna elvers, are kept safely in an exclusion chamber, out of reach from large tuna.

What about the harvest – how did you do that?

Jen: We kept 10 mid-sized tuna that were hung to dry, salted, smoked and cooked in the traditional way. They were consumed during our hākari (feast) with whānau on the final day of the Mana Rangatahi programme. 

Their heads were kept so we could dissect the otoliths (ear bones) and find out how old they were. It’s only a small sample but it provides information to correlate age, length and weight. It is possible that some of the very large tuna could be over 100 years old.

What did the kids think of it?

Jen: For many of them it was novel. Some whānau catch tuna, but these days more western techniques are often used. Although fyke nets were used for the population sampling, there was kōrero (discussion) around traditional catching methods, for example hīnaki, which are woven tuna pots. Our aim is to ensure that traditional techniques, tikanga and mātauranga don’t get lost and are passed down from our kaumātua to the younger generations.

It’s also great to expose the rangatahi to these sorts of things, and give them the opportunity to be around DOC and see what these jobs involve. A couple of them really, really loved it. The project allowed us to identify these individuals that we can include in future kaupapa and mahi that align with their interests and aspirations. As an iwi, we want to nurture that and help rangatahi find pathways that might be future careers for them.

How would you like this project to evolve?

Jen: We want to continue monitoring the tuna population on at least an annual basis. This year was really a pilot study, because we’d never monitored the population on this scale before.

Melissa: It was a really fun project and I learned lots about dealing with tuna. I’m keen to do this every year with Ngāti Apa ki te Rā Tō to better understand the tuna population in Lake Rotoroa. It was also great to meet more iwi members, build our relationship and work together. When we have our methods down, we could survey other lakes like Rotoiti. Monitoring tuna populations, particularly in lakes, is a huge challenge, so empowering and supporting local communities to participate is really important.

Jen: We’re proud of the positive partnership we have with DOC at St Arnaud. In my role as Pou Taiao I’m committed to nurturing and growing this relationship. We want to be able to share the tikanga and mātauranga of the Nelson Lakes area with the DOC staff working in that environment. And then, of course, we want to share it with the world!

More information

The 2022 tuna survey and harvest were part of the Mana Rangatahi programme, a youth programme run by Ngāti Apa ki te Rā Tō at Nelson Lakes. This kaupapa was made possible by Tiaki Wai funding gained through Te Wai Māori and the Department of Conservation’s Bio18 fund.

Aotearoa New Zealand is home to 4 species of tuna. Read more about this taonga species: https://www.doc.govt.nz/nature/native-animals/freshwater-fish/eels/

MIL OSI