Thursday, 24 August 2017

4 Months on - River Irwell Pollution

23rd August 2017

As we near the end of August and slip into the final month of the trout season i had made it a goal of mine to head back to where i first spotted the pollution incident.  Luckily Arthur Hamer insisted we both go, Arthur being a qualified kick sampler it definitely made my observations more accurate.  It would be a 2 part test, checking for insects and also checking for any fish. With 3 rods set up between us, Dry Fly, Nymph and Streamer we could target fish with every method.

Initially reaching the river there was 'positive' signs, take note that when i say positive back when we did the news report there was literally nothing alive, in the air or in the water insect wise. So a positive sign of seeing tiny midges flying around and the odd single Baetis flying around. Nothing much seemed to be on the surface of the water and it was perfectly clear except in the deep pools where it faded into the usual green hue.  We scooted around the edges of the river and found minnows (after netting to confirm) of sizes from a couple of centimetres to a couple of inches. There was plenty of them, in shoals ranging from 12 to a 100. Not the black masses of thousands that we would of seen a couple of years ago, but a positive sign none the less. Why? Because for them to survive there must be a food source as trout can easily switch onto minnows to cover their hunger even the smaller trout with them being so small.

Now it came to looking for insects. We had a good look around for anything of reasonable size and found maybe 2 Mayfly Naiads but as our eyes adjusted on our rock turn tests we found thousands of tiny moving 'worms' maybe 3mm in length at a push. These all clung into the weedy sections of the rock or brick we was observing. There would be literally hundreds of them. With the slimy egg sacs on the same rocks i can confidently say they were Chironomids. Now despite their tiny size it is impossible to age these so they may grow bigger. However it still offers a food supply to the minnows and possibly trout. I do not understand enough of trout feeding behaviour to know if they eat these larva at this stage.

We found a small unnamed brook leading into the Irwell, barely 3 feet wide but i insisted we test it for life and even despite the smoothness of the rocks here, found several cased caddis, olives and a lone Heptageniid. We was also almost taken out by a kingfisher as it raced out of the brook before it halted in midflight and turned back upstream. So it does show that the small inlets, however close the Irwell itself do provide and sustain the bigger insects that we would so often see before the pollution.

The invertebrate life cycle is a complicated one with time scales and all that so come next April it will be interesting to see what changes have happened.

Onto the fishing, well we did about 2 hours of fishing, targeting the main pools and runs where you would guarantee yourself catching a fish. Nothing, on all 3 methods, no sign of trout anywhere. So where are the fish? They aren't dead so where have they traveled? Possibilities are they have moved into or closer to the tributaries which, unaffected by the pollution, would provide a food source. Comparing that to my observations on 'the drain' where trout quite happily sit in the current of an inlet feeding in, it shows that trout would quite happily do this
if it provided a steady rate of food. But you then think, would you rather wait outside the store to get food or go in and get some, meaning some trout will have most definitely pushed up into the tributaries.

Again questioning that, not all fish can move into tributaries, well, at least if you think how many obstructions we have on the Irwell then you would likely find fish trapped between weirs. Trout can go downstream however, regardless of the height of the weir so ultimately they could find somewhere to supply them with a food source. A way i could test this is to fish at as many confluences at possible, maybe 50 to a 100 yards either side of it and also up tributary.

A lot of this information is theoretical and would take much more testing for it to be proven, it also creates just as many questions as answers but one thing it has shown is that there is now some life in the Irwell, but it still isn't the same as we left it before April.

1 comment:

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