Removal of willows hurts eels

Tuna numbers are dwindling as more waterway willows are ripped from riverbanks, the Eel Enhancement Company Ltd says.

Groups removing crack willows along the banks of the Waipa¯ River have hurt local fisheries, company chairman Mike Holmes said.

Removals cause bank erosion, lowering water levels and creating a lack of roots and branches for eels to hide under, he said.

The Waipa¯ Rerenoa Restoration Project has been working with farmers to plant 10-metre-wide riparian strips of native plants.

Its vision, with support from the Waikato Regional Council and the Waikato River Authority, is to restore the Waipa¯ ’s biodiversity

But part of the project involves removing crack willows – a pest species – to make room for native plants.

‘‘They’ve absolutely wrecked the eel fishery out there,’’ Holmes said.

‘‘The willow [removal] is the most serious threat to eel – the single biggest threat. We’ve been saying this for a long time.

‘‘It’s not actually the riparian planting that’s the problem, really, it’s the removal of the willows that’s the problem.’’

Holmes said it would threaten native species such as the New Zealand longfin eel (Anguilla dieffenbachii).

While the native plants look good, they’re expensive and the roots and branches won’t provide the solid structures for the river that eels need for cover, Holmes said.

‘‘How on earth are they getting funding? ‘‘People don’t quite get it . . . If there is no cover, there are no eels.’’

The decline has already been massive, Holmes said. Unhappy eels simply leave.

And it’s not just tuna, Holmes said.

‘‘It’s all the other things like trout. All the fish are gone.

‘‘It’s just a waste of money. It’s like burning money. And that annoys me, too.’’

The O¯ torohanga District Council had concerns, too.

In a letter to the Waipa¯ Rerenoa Restoration Project, the council said the group’s work had accelerated erosion, had taken away most of the shade, increased sediment loads in the river and reduced the number of trout.

But Waipa¯ Rerenoa Restoration Project co-founder Rosemary Davison said a bigger picture was at play.

In two or three years, some of the natives will have grown enough for the branches and roots to provide shade for the eels.

Hundreds of years ago, the riverbanks were lined with flax and ko¯ whai and no willows – the group was simply restoring that, Davison said.

In the meantime, she hopes the eel fishermen will work with the group to maximise the number of eels in the river. Davison said rocks have been used to stabilise the banks. She is also making sure no old native timber – which eels like to hide under – is removed.

Davison doubted trout populations had been affected. Her brother – a trout fisherman – had found plenty, she said.

But she understood eel populations had been a concern and the group would take the matter seriously.

‘‘That is the last thing we want.’’ Freshwater ecologist Dr Mike Joy said eels don’t die when their habitat is removed – they just move somewhere else.

The eels will be back once the native plants have grown bigger, Joy said. ‘‘It’s not like they’re gone.’’

Joy said the real problem lay with commercial eel fisheries exporting New Zealand eel, which he understood the Eel Enhancement Company did.

‘‘When [Eel Enhancement Company] catches them they’re gone.’’