Trapped Auckland dam eels get a human helping hand for epic Pacific migration

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Every year the eels of Aotearoa make an epic journey to spawn in the Pacific Ocean. But eels living in dams need a helping hand, reports Caroline Williams.

There’s suspense in the air as Watercare Dam Technicians Chris Oord​ and Christian Stockle​ drift through the calm waters of Lower Nihotupu Dam in Auckland’s Waitākere Ranges.

Their small sheet metal boat approaches the nets set up a few days before, to catch and transport the eels out of the dam so that they can migrate and reproduce.

Helping the eels is a condition of Watercare Resources’ consent to operate the dam, but it’s more than a formality for Oord and Stockle, who don’t take the responsibility lightly.

Chris Oord has a lot of respect for eels, especially since learning about their migration process.

David White / Stuff

Chris Oord has a lot of respect for eels, especially since learning about their migration process.

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“The more I learn about these things, the more respect I have for them,” says Oord.

Every year between February and June, New Zealand’s long and short eels embark on a journey to spawn.

It’s unclear exactly where the eel spawning grounds are, but scientists believe they are somewhere between New Caledonia and Fiji, said eel expert and NIWA Scientist Emeritus Dr Don Jellyman. .

Once there, the females lay their eggs – 1.5 to 3 million for shortfins and 1 to 20 million for longfins – which are fertilized by the males resulting in a “large number of young” – just a few eels could lead to decent “recruitment”. ”.

After spawning, eels die.

Eels cannot migrate on their own when the dam does not overflow.  (File photo of the Lower Nihotupu Dam during the 2020 drought)

David White / Stuff

Eels cannot migrate on their own when the dam does not overflow. (File photo of the Lower Nihotupu Dam during the 2020 drought)

The larvae then drift to New Zealand with ocean currents over a period of six to eight months – a process that scientists are still learning about. But Dr Jellyman says there’s no doubt the whole migration is “pretty risky” for the eels.

“It’s fascinating. Somehow eels from all over New Zealand somehow manage to arrive at the same time to do this thing.

Oord says elvers (baby eels) and adults will “happily” climb in and out of Nihotupu’s lower dam when it overturns, but need human help when it doesn’t.

Oord and Stockle start pulling in their nets to see if they’ve caught any eels. HAS ThingsThe visual reporter of put on his wetsuit and waded through the dam for nothing?

Hit. Seventeen eels were captured.

As the men transport the eels in their boat, things start to get “slippery” with slime, secreted by the eels as a defense mechanism. It also keeps them moist, allowing them to breathe through their skin when out of the water.

Back on land, eels are assessed for physical signs that indicate they are ready to migrate, including a blue ring around their eyes to help them see in deep, dark parts of the sea and elongated heads to make them more profiled.

Their stomachs also change color from yellow to silver, so watching predators mistake silver for daylight.

Watercare dam technicians Christian Stockle and Chris Oord check for eels.

David White / Stuff

Watercare dam technicians Christian Stockle and Chris Oord check for eels.

The first eel weighs 1.8kg and – after a gentle struggle for the eel to straighten up – is 72cm long. It is considered by Oord to be “definitely” migratory.

Stockle helps put the eel in a large tub, covering it with a wet burlap netting while she waits for her mates to be measured.

The next eel is a much smaller 250g, like a “pet eel,” says Oord. It doesn’t show any of the telltale signs that it’s ready to breed, but it’s still being measured, so the data can be passed on to the Ministry of Primary Industries.

“All data is good data.”

Chris Oord checks an eel for signs that it is ready to migrate.

David White / Stuff

Chris Oord checks an eel for signs that it is ready to migrate.

Back in the dam it’s fine.

And then, a brief moment of panic – at least for this tricky reporter – as several of the yet-to-be-measured eels squirm out of their tubs and attempt to follow her to freedom. One succeeds.

“Things never go perfectly when it comes to animals. You’re fooling yourself if you think you’re holding one in your hands,” Oord says of the slippery attempt to catch the escaped eels.

By the time Oord and Stockle examined them all, eight migrating eels had been identified, three of them longfins. The largest of the transport weighed 2.3 kg and was 85 cm long.

Each eel is weighed and measured, even if it is not migratory, because the data will be useful to the MPI.

David White / Stuff

Each eel is weighed and measured, even if it is not migratory, because the data will be useful to the MPI.

The tank of eels is then taken to an estuary in Manukau Harbour, where there is a good mix of fresh and salt water, to help the eels adapt.

Dr Jellyman says people are increasingly recognizing the importance of helping eels to migrate, with most species being threatened.

“Anything we can do to improve the migration of eels to the sea is worth it.”

The Department of Conservation considers short eels, which are also found in Australia and some Pacific islands, to be a non-threatened species.

Migratory eels are released into an estuary in Manukau Harbour.

David White / Stuff

Migratory eels are released into an estuary in Manukau Harbour.

However, the endemic population of Aotearoa long eels is in decline, with human activities such as pollution, loss of vegetation near habitats, overfishing and dam construction all having an impact.

Ngāti Haua’s Hone Pene​ published a thesis in 2004 on exhaustion Tuna (eels) in the Waikato due to commercial fishing and pollution.

He says tuna has long been a highly respected product taonga (treasure) and a special treat for me and tangata whenua.

Watercare is needed to catch and release migrating eels to operate the Nihotupu lower dam.

David White / Stuff

Watercare is needed to catch and release migrating eels to operate the Nihotupu lower dam.

Legend has it that Kupe, credited by Maori as the first person to discover Aotearoa, once saw “a beautiful tuna ‘swimming in the river’ and the rest was history”.

During Pene’s childhood, tuna fishing was one of the first occupations of whānau to marae Where Tangihangaso that manuhiri (guests) were able to enjoy “the best of our delicacy Kai”.

“If you have eels/tuna on the table, it’s like ‘wow’.”

Pene said in Morrinsville, where he grew up, iwi would “step back” after the first big post-summer rain, to support people during the migration.

Wednesday's transport sees eight migrating eels identified and released into an estuary.

David White / Stuff

Wednesday’s transport sees eight migrating eels identified and released into an estuary.

“If we don’t let them go, it’s game over. It’s not just about our generation, it’s about our tamariki and mokopuna come.”

Nowadays, up to 137 tons of native eels – including longfins – are caught by commercial fisheries and sent abroad as food.

As Oord and Stockle release migrating eels from the Lower Nihotupu Dam into the estuary, there is a real sense of accomplishment.

The pair have caught and released a total of 44 migrating eels from West Auckland dams so far this season, which is in its final days.

If these eels decide they don’t want to migrate, they can live happily in the estuary or find their way back to the dam. Any migrating eels in the dam that were missed will have another chance next season.

And once the offspring of this season’s migrating eels find their way back to New Zealand, Oord and Stockle will be there to help them get back into the dam.

Stockle says they both enjoy working with eels.

“It’s definitely one of the best parts of the job.”

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