Week in Review

Another nail in the coffin for endangered eels

Turbines in hydroelectricity dams are mincing eels. A bill aimed to protect indigenous fish is likely to exempt the dams from regulations which could force measures be taken to save the eels.

Conservationists say a bill aimed to save freshwater fish fails to protect thousands of eels from being minced in hydroelectricity dam turbines.

Environment Committee recommendations to The Conservation (Indigenous Freshwater Fish) Amendment Bill suggest existing hydroelectricity dams be exempted from a clause regulating them.

Reasons given in the committee’s report are that there aren’t many hydroelectricity dams in New Zealand, the issues of fish passage are already understood, and owners have almost no options to mitigate the risk.

Forest & Bird freshwater conservation advocate Annabeth Cohen thinks the industry should be taking the lead by implementing best practice solutions, rather than trying to avoid regulation.

“If they understand turbines and hydroelectric dams are killing all migrating female longfin eels and they know longfins eels are endangered, they need to be taking a step in the right direction to stop these eels from getting minced up and killed on their way down.”

Longfin eels’ life cycle depends on migration. Once they reach around 30 years of age, they travel down rivers and out to sea to spawn near Tonga before dying. The young return to New Zealand and migrate upstream to live.

For female longfin eels, which are larger than males and fat with millions of eggs, the turbines are particularly deadly. It’s estimated all are killed by the blades.

With a population classed as at-risk and declining in numbers, and commercial fishing legal, Cohen said hydro dam deaths are “enough to warrant a major concern”.

"These eel are partially in trouble because their habitat has been destroyed over the last century with wetland drainage, irrigation and drainage infrastructure – these dams are adding to their decline by killing nearly all migrating female eels."

The Karāpiro mincings

Erin Hampson-Tindale is a keen trout fisher. He’s become so incensed he’s started a Facebook page Dammed Eels where he posts photos and videos to raise awareness of the issue. 

He’s spent nights at the base of the Karāpiro dam, watching mutilated eels wash up.

“You can watch the water with a spotlight and you might get a whole bunch of them come down at once. You might see dozens chopped up. Half eels, still alive wriggling around. Dead eels, some chunks of the bigger eels. Small eels that are still whole but they’ve been smacked about, they’re sort of wriggling around dying slowly.”

Eels need to navigate several dams on the Waikato River to make it to the sea to spawn. Image: Getty Images

With Karāpiro being the final dam in a series of eight on the Waikato River, he worries about what’s happening at the other seven.

He’s contacted Mercury, which owns the dams on the Waikato River.

“What they keep saying is they need to talk to the other stakeholders of the catchment and discuss other issues like water quality, habitat, people digging drains.”

He feels this is passing the buck. Clear water won’t stop turbine blades.

“The turbines are the problem, the eels are screwed, they’re not getting out of there.”

He thinks Mercury should fund trap and transfer programmes like some other electricity companies do and move mature eels below the turbines.

A spokesperson for Mercury said it monitors eel deaths below dams and is currently working with partners such as iwi, the Waikato Regional Council and commercial fishers on eel management issues, including identifying "practicable options to enable transfer of migratory-sized eels downstream".  

Mercury’s submission to the bill's select committee states it is impractical to retrofit fish passage. It asks that regulations not be applied to existing structures related to a hydroelectric power scheme.

It notes all eight dams are currently exempt from needing a fish pass or fish screen as current rules give an exemption for dams with water rights issued prior to 1984.

"The challenge of getting eels downstream through hydro dams is a global one and to our knowledge has not been fully solved for any large dams worldwide. Where isolated solutions have been found, these are generally specific to the dam and the particular catchment environment," a spokesperson told Newsroom.

"Mercury supports science-backed action, and fisheries experts agree that this is a difficult science due to the unpredictability of the eel behaviours and the way that hydro dams are constructed specific to each site."

What are the options?

There are a number of ways to help fish travel downstream when dams block the way.

Trap and transfer is one and is a method funded by some electricity generators.

Other options include: turning the turbines off, spilling water and fish, using larger turbines, adding physical barriers or deterrents and, installing bypasses.

Karāpiro dam. Photo: kiwinz Flickr CC BY 2.0

Mercury’s Karāpiro dam has a bypass installed in 2013 which it said has not been successful. This year only one eel was caught in a holding pen it feeds into. It thinks this was due to not activating it early enough in the migration season. Despite the lack of success Mercury said it's still being trialled.

Fish and Game’s Auckland/Waikato fisheries manager Dr Adam Daniels said the bypass was ineffective in the way it was implemented. He’s a former engineer for the United States Army Corps of Engineers and has spent a decade looking at dams and fish passage.

“Imagine you have a bathtub, and a drain at the bottom. It’s going crazy and you have a straw somewhere near the top. If you’re sending particles through, almost none of them are going to go through the straw because none of them are going to find it.”

To attract an eel to the passage, or straw in Daniels’ analogy, enough flow directed to the straw to attract the eels to it is needed. He said this would need to be “at least a third of a river” diverted away from electricity making turbines. Barriers to the turbines would also be needed. 

He thinks retrofitting a dam with a workable solution could easily cost $10 million.

For spilling water, and hopefully fish attempting to migrate with it, he gave the Columbia River as an example. By law, dam operators have to spill 60 percent of the river in some areas at times of the year. He said that means over $1 million per hour in lost revenue.

For New Zealand’s eels during migration season, spilling water at night after heavy rains - which triggers the urge to migrate - may save eels from turbines.

Daniels suggests an easier solution might be discouraging eels from the area completely, and restoring turbine-free wetland habitat.

He thinks the reason Hampson-Tindale is suddenly seeing so many minced eels is due to the elvers (young eels) the eel fishing industry is transferring above the Karāpiro dam.

An avalanche of minced eels coming

Since 1992 the Eel Enhancement Company, an organisation representing North Island’s commercial eel industry, estimates it has caught and transferred 37 million elvers from the base of Karāpiro dam during their attempted upstream migration. Two tonnes were caught last year alone.

The largest portion (38 percent) were transferred above the dam in Lake Karāpiro. The rest were distributed in six other lakes.

“They’re basically using those reservoirs as aquaculture. The downside to that is a lot of the adults, the ones you don’t catch, are going to die,” said Daniels.

The first of these eels transferred back in 1992 are likely to be reaching sexual maturity. He imagines the number of minced eels found beneath dams will increase in the coming years.

Eels found below Karāpiro. Photo: Supplied

Hampson-Tindale plans to use a boat to collect dead eels below Karāpiro next migration and asks people to do the same beneath other Mercury run dams.

He worries the dams are another nail in the coffin for at-risk longfin eels which are already subject to commercial fishing.

If the bill passes and hydro electricity dams get an exemption, he thinks longfin eels deserve some help.

“It’s time we throw our native species a bone and ban the commercial fishing of them.”

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