Temperature effects on Brown trout.

[whinging pom]

Hi Pom

Local policy, but basicly all the salmon rivers follow it. It is rooted in data like these:
https://pubmed.ncbi.nlm.nih.gov/26179562/

And being evaluated at least once a year. The river I fish most for salmon, Skjern closes at 18 degrees and opens again when the water temperature drops below 16,5 degrees. This can lead to weird scenarios, where the river opens and closes due to cold nights and warm days.
The freezer filling is on a quota, and this year they split it up in three batches, first one was fished up early May, and second starts tomorrow. Two days ago the water temperature was 17,8, right now its 15,87 so it will probably open.
https://skjernaasam.dk/uncategorized/va ... -den-16-6/

Common sense isn't so common here too, bitching about closure happens here too

Cheers
Lasse

Hi lasse thankyou ,
i like the clearly worded rules and no ambiguity, and that's what I'm trying to steer the club to adopt.

When i did the read out from the data logger and saw the peak on the graph my heart sank, not for the trout so much , but the inevitable saga that would ensue, which is becoming an annual event in my calendar.
Ive now been up 6 hours on a work day and been dealing exclusively with this.
So I am determined we can add an extra rule on the club membership and my energies and enquires can then be focused on alleviating the negative effects of this climate change on our speckled buddies in the stream who enrich our lifes.

Anyway no rain, more heat I'm off down the stream with my thermometer to check the latest. And who knows i may get chance to swish the MPR and practice pull back for a while ( its great at trying to zap house flies off the walls while my foots in a surgical boot, Im missing, but getting closer to my first kill!!)

thanks as always
Pom

[whinging pom]

IMG_0157.png (144.4 KiB) Viewed 1303 times

Im about to order more data loggers for our brook

What loggers are you using?
Been thinking of trying to build my own Pi based one to test our lakes.

Alan

hi we’re using Gemini tinytag logger like above
Simple and very adaptable , I measure every 15 minutes to build up a picture over the seasons, which is not stretching its memory at all and the batteries last for a year or two
Pom

[Paul Arden]

Very cool. I didn’t know such things existed. A few questions

Have you tried measuring temperatures in different parts of the river and do they vary? Eg eddies vs main current? Depth vs surface? Or is it all pretty similar?

I assume you measure daily in the summer?

What a great tool.

Cheers, Paul

[alanj]

Many thanks pom, Those look really good. One for my pond even if I can't convince our club they need some for the lakes.

Cheers
Alan

[whinging pom]

It lives secured by trace inside that block at the lowest end of our stream under a low road bridge hidden from sunlight and the eyes of some of our travelling ‘visitors’ who like to nick our Trout and anything else that looks like it could be of value.
I leave it to do its work and once a month go down with a lap top and connect it up and download the latest set of readings . You can program it to read as often during a day or week as you like. I thought every 15 mins, on a whim really thinking the curves on the graph would be smoother and more sinuous. As it I’d you can see if cloud cover or a rain showers come over and the fluctuations.
The plan is to have another few placed in convenient places to visit and log on to the lap top.

I’ve been at the club to buy them for years, but they dragged their feet. My mantra of the more things we monitor and the longer we do it, the more we know and the stronger our hand if anything goes amiss.
As these summers have changed it would have been great to have had some realistic charts of what we have been through in previous years. All we had to discuss fishing policy was some Environmental agency readings done a few times a month at indeterminate times of day to get a yearly picture but missed the peaks and the recovery periods.

The next step now I have shown the value, will be the top end of our fishery in a similar position, then as I do habitat work and add more shade to the steam along the banks we can see how the stream reacts over the length.
I’ll have one in the air to read ambient air temps to over lay that data on the graphs.

It would be interesting to have some at the bottom of deep pools the logistics of getting them secured and down and the inconvenience of retrieval for downloading the data is the limiting factor, it’s not really the info I need.
I have been along in the past with probes measuring just sub surface water and river bed water and there was virtually no difference, especially in the pool and riffle sequences where the water is tumbled

( the first I saw of these used was on an experiment to line a stream with trees and watching over a few years how much the temperature dropped at the lower length in comparison, it was several degrees).

I’m now starting to use a Dissolved oxygen meter to get a picture through the stream of the variation above and below the various types of water and feature. So I can find ways of increasing it by localised habitat work and so that maybe we can predict what the overall picture is based on the Temp readings at either end of the fishery

I could go on and on

A friend has three set on a old remote spring fed stream where there are some very rare caddis, the spring is virtually a constant temperature, he has one a metre from the spring, one mounted on a pole for the air temps and one a good distance downstream. The pictures he gets with that of how the water closely and quickly reacts to the localised weather events is quite eye opening.

One of the pieces of advice given to fishermen in warm weather is just fish the mornings and evenings when the waters cooler. Looking at our readouts however the peak of temperature is just before midnight. But that’s our stream.
WP

[whinging pom]

The dissolved oxygen reading: brief explanation.
Yesterday the stream was 19.5 - 20.5c which is the starting to get uncomfortable and feeding and growth affected range and not great for recovery of catch and release. They can survive this fine for some time but if the oxygen drops and ammonia increases it can be fatal.

Our DO reading was 8.2 ppm which is above the comfort zone , 12 is optimum and 3.5 is potentially lethal. If there was a traffic light system we would still be above amber.
Pom

[whinging pom]

It has just been announced that June was the hottest on record in the UK.
Last year In The UK there were 6 incidents of mass fish deaths due to water temperature, In June alone this year there has been 60 recorded incidents.

We witnessed with the data logger a phenomenon counter to common sense. That when we finally got some rain and fresh water in the Brook, Instead of cooling down the water temperature, it immediately jumped up 1.5c warmer (a river keeper in Scotland says he sees the same jump in heat waves.)

Warm rain falling on hot ground and running off into the river pushing the temp sharply up is what we are assuming is the cause is.
A fish wipe out in the River Cam in Cambridge a few weeks back was directly after the long awaited rains arrived.

thankfully we've had a week of largely over cast skies and cooler wind and the temps from 21.5c peak have at last returned to 16c and ive opened fishing again for the members.
best
Pom