No juveniles last year

rfcellis

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Joined
Jul 5, 2012
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679
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London
Hi all,

Our electrofishing in October 2018 revealed few baby trout and no fingerling grayling - rather a worry. The catch returns don't give any cause for greater optimism.

I was wondering if others had found the same thing? Are we an isolated incident? or was it a bad year for trout and grayling spawning?

There are plenty of possible reasons but it would be useful to know whether we are an isolated case (i.e. how we re managing the fishery or the state of our river) or whether it was a more common issue for example driven by extreme summer temperatures.

Our club's stretch of river is a small chalkstream with flows much lower than they used to be and the river hit 16 degrees (4+ degrees warmer than normal)).

Thank you for any insights.

Cheers
Richard

- - - Updated - - -

ps - the gauge shows water levels in 2017 were even lower... View attachment Gauge levels.pdf
 
G

guest54

Guest
Way back, when I knew no better, I kept young trout, sourced from a local stream, in a large tank with a strong flow and a cooler which kept the temperature below 8 degrees. The cooler failed and every trout keeled over as the temperature rose, experiment over and never repeated. This summers high temperatures and low flows must have had a similar effect on juveniles in many streams. The local stream those young trout were sourced from was bone dry this year, by which I mean zero water. I doubt there is a single trout left in that stream.
Remember though that young trout will hide under stones in the faster water in hot weather and may not show on a survey.
 

liphook

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Mar 23, 2011
Messages
327
Increased temperatures and reduced flow rates are always your enemies. Also I'd avoid electro fishing as a means of surveying as it's effects, particularly on juveniles, are questionable
 

raphael

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Feb 13, 2010
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France, near Sancerre
16°C is not so much, it is right in the comfort zone for brown trout... But given the conditions Europe encountered last year, summer was not favorable for salmonids. Low flow is always damaging for young fish which can not find shelter from predators, it exacerbates competition and density-dependance and all these negative factors. Result is very poor survival of 0+
 

BobP

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Oct 28, 2007
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Wiltshire
Juvenile brown trout and grayling are not the easiest things to capture by electrofishing. This is a method that performs best with larger fish due to the way the electricity acts along the length of the fish. The longer the fish the greater the attraction to the positive probe.

Juvenile grayling are especially difficult to catch in any number. On many occasions when surveying I have seen shoals of 0+ grayling in shallow water and have popped the anode right on top. The result has been two or three out of maybe 150.

Juvenile brown trout tend to bury themselves in any sort of cover. Beds of cress are a real favourite, but other weed beds and tree roots are also hot spots. Under those circumstances they are only too easy to miss.

16 degrees is not going to be fatal to either species. I fished a river in Austria several years ago after an extremely hot summer. This river was fed principally by a lake and the water temperature went well over 20 degrees. The river held rainbow and brown trout and grayling. The grayling and rainbows were OK but the brown were dying of BKD which is a kidney disease triggered by high temperatures and stress.

You need to consider that last year was a very difficult one. We had the bitter weather in early March which is when the trout fry would have been emerging from the redds followed by weeks of below average water temperatures. The Test fished absolutely rubbish well into May, and the upper Avon ran brown until June. I would suspect that the river conditions and temperatures may well have disrupted the grayling spawning in April.

Then we had the long hot period which I doubt bothered the fish too much, low flows notwithstanding. The fish survived 1976 well enough and 2018 was nowhere near as bad as that.

One year's survey results is not enough to base any sort of conclusions on. If you do this survey every year then you will notice peaks and troughs and this is normal. Grayling, being shortlived, are especially prone to the boom and bust cycle. Keep careful records of what you catch on the day including water temperature. Keep records of river conditions throughout the year as well because it is all too easy to forget what went before and that can hold vital clues.

Above all, don't forget that a survey is only as good as the people doing it, and it is only a snapshot of what is there at the time. Go back in a week and the result will be different.
 
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Mr Notherone

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Jul 19, 2013
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Monmouthshire
I took a reading on the Usk last summer of 23 degrees. I don’t think that 16 degrees in itself would have been problematic.
 
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