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The latest moves in 'conservation' - update...


Amarinus

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It sounds like it is pretty nasty stuff and would completely destroy the whole ecosystem making it very hard to introduce fish again until everything has started to return, you also have to wonder about how long it hangs around and also the effect on the water of all the fish and inverts dying and rotting away.. They will also wipe out alot of natives because they wont be able to catch them all to save them.

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I would love to see them rotenone Karori.

Rotenone is a plant-based toxin, another name for it is derris dust - you can buy it at the supermarket.

It is used extensively overseas, especially in the US, and has been in commercial use for the last 150 years. It is used as a pre-harvest insecticide on food crops, and many other uses.

It degrades fairly quickly, the rate depends on various things but usually a matter of days to months, and is considered to be 'environmentally benign'. It is used at very low rates (~1ppm) but dosage depends on species, turbidity of the water, and lake bottom complexity.

It affects fishes' gills, blocking oxygen uptake and causing them to surface. Fish are then easily caught and if placed in fresh clean water most will have a full and fast recovery. It is preferable to catch the fish as they surface as an enormous rotting pile of fish is not going to help the lake ecosystem.

It is an insecticide and can kill off aquatic invertebrates, but these usually recolonise incredibly quickly due to flying adults or drift from upstream, just as in the wild after a massive flood.

The Karori lower reservoir is completely [hmm, swearing is objected to here... you get what I mean] by perch. It is pretty much a perch-only system. The little perch eat the zooplankton (daphnia etc), which releases the phytoplankton (green algae) from herbivory, which is why the lake is subject to really bad algal blooms, and has helped the cyano take over.

Brendan Hicks et al from Waikato have been intensively fishing the lower reservoir for years, I think at least the last seven, and removed a huge weight of perch using both netting and an electrofishing boat. Of course larger fish are caught more easily, so this has resulted in a major size skew, with far more of the small zooplanktivorous fish now which is potentially compounding the phytoplankton problem.

There is absolutely NO WAY the perch can ever be reasonably controlled or eradicated without the use of piscicides.

Apparently in the upper reservoir and in the streams that lead into it there are still banded kokopu. Given how long ago the reservoirs were built, and how to outflows are constructed, it is highly unlikely that any of them have come from the sea, so they have managed to form a landlocked population. Get rid of the trout and the bandeds will be able to take over again - trout have a strong predation effect on galaxiids under 10-15cm.

An amazing example of the use of rotenone in NZ is Lake Parkinson near Auckland. In the 1960s exotic weeds got in (please note: most problem aquatic weeds in NZ were released from aquaria) and rudd and perch or tench were released illegally. Within 10 years the lake was mostly weeds and the rudd had destroyed the put-and-take trout fishery. They put in grass carp to sort the plants in the early 1970s, and after 6 years all plants were gone, including those that could grow back from rootstock. They rotenoned the lake and removed all the fish - the grass carp and trout were revived in clean water. Over the next few years the native plants regrew naturally from the seed bank in the sediment (exotic plants do not have both sexes here yet, so no seeds from them).

A very interesting report prepared for DOC by a Waikato native fish scientist: http://www.doc.govt.nz/upload/documents ... SFC211.pdf

Also a paper on Lake Parkinson: http://www.doc.govt.nz/upload/documents ... /aqua5.pdf

So far most of the comments have been very negative but with little actual content or reasoning. I would like to know exactly what people are objecting to so we can have some actual debate.

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Fear of the unknown I suppose....

Rotenone's ability to degrade that fast is probably one of the best reasons to use it. That and it has been used for decades overseas and there is plenty information and evidence of its use being successful, with subsequent rehab being much more successful.

I didn't bother replying as the tone of the thread was clearly anti rotenone with no real reason, only opinion and speculation.

Do we really think DoC makes decisions based on a simple coin toss?

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So far most of the comments have been very negative but with little actual content or reasoning. I would like to know exactly what people are objecting to so we can have some actual debate.

not really fair, livingart posted a link to that factsheet. that outlines some very reasonable things to object to. you seem to know a lot about the issue and that is great. all we had was the original article.

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I'd just like to add to this post, seeing as I will be helping with this operation in Karori.

Stella pretty much covered all the basics so no need to repeat myself too much.

I've read the proposal in detail and will vouch for its validity as a treatment for eradicating pest fish. People involved in this, and people who have reviewed and approved the proposal are experienced conservationists and scientists from multiple institutions (not just DoC). The plan is well thought out and has exhausted all possible ways to mitigate any risks to the ecosystem. In short, the stream will be surveyed on several occasions to establish accurate population estimates of banded kokopu. Prior to the treatment, as many possible natives will be caught (through electrofishing) and released into the upper reaches of the stream where no trout as present (behind a temporary barrier so they can't swim back down before treatment finishes). Rotonene will then be slowly dosed from the barrier down the stream killing everything in its path all the way to the reservoir at the end. Control trout will also be present in cages in the reservoir so that the minimum dose of rotonene to cause all of them to die will be detected. All dead fish will be removed.

As Stella mentioned, rotonene degrades quickly making it an excellent tool. After the stream is cleared as safe, the barrier will be removed, and the natives from the upper reaches will begin to migrate back down into the newly establish pest-free ecosystem.

This method has been used successfully in the past and hence why it is being considered as the best method for restoring karori's waterway back to a natural system.

I'd also like to remind everyone that the people who entered this line of work didn't fall into it accidentally and didn't get into it because they hate nature and want to kill things. They studied for many years and are passionate about animals and conservation biology. They are the best people to be making these decisions as they have the knowledge base to back it up. Some methods may seem harsh, but someone has to do the dirty work. As always, these proposals are publicly advertised and submissions can be made if anyone has concerns that they believe the experts overlooked.

Oh yeah, and stuff.co.nz pretty much botches ALL their stories anyways (except for the stories they copy directly from the journalist bank). Stopped reading that garbage a while ago...

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Haha wish it was that easy! Unfortunately, won't be able to eradicate all of them like this :(

We were joking of 'harvasting' some brown trout with some electrofishing before administrating the rotonene :P Not sure if they are approved for human consumption though!

Could just let anyone with or without a fishing license to get the trout out :lol: im sure all the kuzzy's wont mind doin it for DOC :lol:
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