Scientists respond to Feds’ claim that trout are cause of water decline

Invasive trout blamed for poor water quality — are farmers off the hook?

Press Release by Science Media Centre at  6:49 am, 05 Jul 2011

Scientists are questioning claims by a prominent dairy industry representative, suggesting trout are a ‘disastrous species’ — no better than ‘freshwater stoats’ — and that farmers have been unfairly blamed for their impacts on declining water quality.

These allegations were made in a speech last week by outgoing Federated Farmers chair Dairy chairperson Lachlan McKenzie, urging members to use science and their own judgement to distinguish fact from opinion.

Professor Colin Townsend, Dept of Zoology, University of Otago comments:

“In his speech, Lachlan McKenzie advises us not to accept someone’s opinion as gospel but to interrogate it and check it out. ‘If robust it will stand scrutiny’, he says, ‘if not, there is cause for concern’.

“As a researcher with 40 years experience and someone intimately involved in both trout research and the effects of agriculture on stream ecology I wish to comment on a few relevant points.

“Our research has shown that by reducing grazing by stream insects, trout can lead to a modest increase in algae on the streambed. These extra algae have the effect of sucking up some nitrogen from stream water and so the trout actually make a small contribution to cleaning up the mess caused by nutrient runoff from farms. In any case, the small changes to nutrient fluxes in streams associated with trout are swamped by the much larger amounts of nutrients entering as diffuse pollution from the land.

“It’s worth noting too that our research in Otago shows that soil erosion, and the resulting smothering of the streambed by fine sediment can be even more harmful to stream health than nutrient enrichment. Unless Lachlan McKenzie has witnessed trout emerging from streams and churning up the land with their big fat hooves, he will find it difficult to shift responsibility from cows to trout.

“Farming is important to New Zealand but so is the state of our environment. Thankfully, many farmers are already doing their best to be good stewards. What is needed now is more discussion, education and collaboration between all sectors with an interest in land and water management, not an untutored and distorted analysis of the evidence.”

Professor Angus McIntosh, Chair in Freshwater Ecology, University of Canterbury comments:

“I have studied the influence of trout on native biodiversity for most of my career, and as a researcher, I’m also involved in developing ways to mitigate the effects of land-use intensification on waterways.

“Yes, it is true that trout have negatively influenced native biodiversity and they do alter nutrient cycling. However, to compare their effects to stoats, and to imply they are somehow worse than, or equivalent to, the effects of land use intensification on water ways is a misrepresentation of the science.

“Firstly, they are clearly not ‘eating the basis of the food chain’ since we have highly productive trout fisheries in clean water streams. Native fish populations have been affected, but the resilience displayed by stream invertebrates in supporting predation by both native and introduced fishes is remarkable. Secondly, the effects of nutrient enrichment on algal accumulation and nutrient cycling are much more powerful than those of trout.

“Experiments conducted in New Zealand and elsewhere clearly establish that elevated nutrient concentrations quickly overwhelm any effect of trout on algae, which is actually small by comparison. Trout have not been responsible for what could be described as ‘algal blooms’ in New Zealand or elsewhere. Moreover, the effects of nutrient enrichment on stream invertebrate communities are also likely to be much stronger than those of trout. …

“The health of water ways in places like lowland Canterbury is very poor at present. The primary causes in agricultural areas are high sediment levels, low flow and high nutrient levels. In urban areas, storm water contaminated with heavy metals and sediment (especially since the earthquakes) are to blame. Discussion regarding urban and rural waterways should be revolving around plans for rehabilitation and management, and needs to based firmly on the best science possible.”

Prof Jenny Webster-Brown, Director — Waterways Centre for Freshwater Management comments:

“Trout may be an introduced species, but they are also the most sensitive species to most contaminants, and the first to show the effects of water quality decline. Because they are widespread globally, there is also a great deal of toxicity data (data that tell us when a particular species will be affected by increasing contaminant concentrations) available for trout; certainly when compared to the data available for species which are endemic to New Zealand.

“Trout are therefore a very useful indicator of water quality, and protecting them ensures an additional level of protection for other species from the effects of poor water quality. “

I spoke on the science of declining water quality at the Fed Farmers Conference last Thursday. My PowerPoint presentation from the speech is available as a PDF here.

10 Comments Posted

  1. I wonder how your speech was received Russell. You would hope that some of those attending the conference would have offered their congratulations and agreed with much of your presentation.

  2. To be fair, it is also true that detergents, shampoos etc put in a lot of phosphate from water-based sewage schemes – which most still are. This does not excuse FF from their culpability, but it is definitely a factor in water degradation.

  3. Lachlan McKenzie’s firing a shot at Fish & Game NZ.
    I wonder what his strategy is?
    Re-igniting the ‘Dirty Dairying’ fight?
    Or did he just have a red-blooded ‘alisdair’ moment?

  4. Shunda says “Photonz, I just read the speech, and if anything it only strengthens the original post Russell made”

    I agree.

    I just thought giving just a two word quote, without even the sentence it came from, is nowhere near enough infomation for us to make an informed opinion.

  5. Photonz, I just read the speech, and if anything it only strengthens the original post Russell made.

    This guy is typical of the arrogance and anti NZ attitudes of the feds.

    These people are proud, defiant, and extremely intolerant of anyone not in the industry, they claim to be ‘the back bone of the nation’ and they mean to use this claim as a rod on the back of the rest of us.

    The claim is bullsh!t in perfect keeping with the other bovine excrement that proceeds from the mouths of these people.

  6. Thanks for the link photonz. Reading the speech, it is hard to tell if McKenzie is being deliberately confusing or is just thick. A bit scary that he was on the land and water forum since he doesn’t understand limiting nutrients. The reason waterways are P-limited rather than N-limited is because N is so excessive, not because the problem is too much P as McKenzie claims. He obviously hasn’t read the McDowell paper he refers to (R. W. Mcdowell, S. T. Larned & D. J. Houlbrooke (2009): Nitrogen and phosphorus in New Zealand streams and rivers: Control and impact of eutrophication and the influence of land management, New Zealand Journal of Marine and Freshwater Research, 43:4,985-995). I wonder who wrote the speech?

  7. Ruseel – I notice you don’t actually tell us what McKenzie actually said.

    All you give us are two word quotes without even the benefit of the sentence that surounded them – you fill that in with your words.

    Yet you give us 12 paragraphs of word-for-word quotes countering the four words you have supplied us from McKenzie.

    Unless you are trying to con people, can you please give a link to Mckenzies speech.

  8. If you are losing the science argument I guess the only thing left is to make up some science to buy some time. It worked with climate change….

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