What are the River Exe Rainbow Trout eating?

Back in February I opened up a bit of a can of worms with my blog Panic! Rainbow Trout invade the River Exe.   It was all to do with the great flood of Saturday 22nd December 2012 when the Exe rose something like 24” above any previous level recorded since the 1960s.  This event had a devastating effect on many local businesses in the community, not to mention households, some of whom have only just returned to their premises.  Meanwhile fish farms situated along the middle Exe were swamped, including Exe Valley which has been producing Trout for well over 100 years.

The net result was a very large escape of triploid (infertile) Rainbows; the like of which has never been seen before.  As news of the break out travelled and buoyed on by a special EA dispensation allowing fishing prior to the usual open season on 15th March, the banks of our river became crowded with anglers casting all manner of flies and spinners at these invaders.

There was a lot of speculation about how many fish really entered the system but there was certainly no doubt that the following weeks resulted in some huge hauls of Trout numbering 20, 30, 40 and even 50+ in a session.  But of course while I am sure that some were secretly quite enjoying this opportunity, others were far from amused.  Check out the comments section attached to my original blog and you will see what I mean!

It was only natural for anglers to be concerned that this huge influx of non native fish could spell disaster for the Wild Brown Trout, Grayling and of course Salmon which roam the this great river.  Even so, with words such as “Ecocide” being bandied about and threats of legal action against the perpetrators of this evil act (who, Mother Nature!?) I decided that I would put my own thoughts forward via the blog.  Take a look for a bit more detail but in short I offered the view that while none of us were exactly happy (not least the fish farmers – who also fish for Salmon themselves) about the escape, it was probably not quite the disaster that was being predicted.

River Exe Rainbow Trout showing stomach contents

Sticks & Stones … seemingly the diet of choice for a River Exe Rainbow!

In particular I was not convinced that the stock fish mentality of the Rainbows which had escaped would equip them with the necessary skills to survive in the wild.  Take a look at the stomach contents of one of the many landed while guiding this year and as we can see this poor Trout was sure that sticks, stones and weed should provide it with enough nutrition! But there are still fish out there, so the question has to be “What are they eating to enable them to survive?”

Reports suggest that it is certainly not the Salmon Parr that were predicted to become their main source of protein and despite spooning and gutting many fish myself during the season I haven’t found much in the way of insect life, let alone Parr.  So could it have something to do with their previous life as stock fish?  Back in their more familiar ponds these fish enjoyed a diet of high protein pellets without really having to work for them, resulting in large stores of fat.  After all, isn’t that what a Salmon uses to survive during their journey?

It’s only a theory of course but it would explain how these fish have been able to sustain themselves for so long.  In fact even during the summer heat wave which proved incredibly tough for the fish in the lakes, the fish in the river seemed in relatively good shape, no doubt enjoying the high oxygen content, lower temperatures and space.  Many of the fish which I have cleaned recently now have firm (white) flesh, very little in the way of fat and razor sharp tails.  Hook one on a 4 weight and it’s not uncommon to watch the backing disappear through the tip ring!

All great fun but I feel sorry for the remainder of these fish because they have had a full season to learn to survive in the wild and so far this seems to have been without learning to feed themselves.  How long can they keep going on their fat alone?  Some are already falling by the wayside and there are the long winter months ahead to endure before things may get better.  To stand the chance of surviving until the spring these Rainbows will have had to become skilled in hunting for their own food which I personally believe they are incapable of doing.  Sadly it is a long, slow death which awaits them … that is if the Goosanders don’t get them first.  I observed a troop of these birds that survive on a diet of fish nonchalantly cruising up the Exe recently; which really is a cause for concern.

A River Exe Rainbow Trout caught on fly

One of many pristine River Exe Rainbows caught this season

I would love to hear your views on the subject and so too would Stuart Priddle of Blackdown Environmental who is currently studying the economic & ecological effect of non-native trout entering the River Exe.  This will form part of his MSc degree and includes a questionnaire available in a variety of formats.  If you would like to put forward your views please Contact Stuart by Email. All completed questionnaires are anonymous and you will not be identifiable in the subsequent report or publications to follow.  I for one will be fascinated to read Stuarts findings.

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2 Responses to What are the River Exe Rainbow Trout eating?

  1. Hi Nick. You may recall that I fished the Exebridge Fishery beat for an hour or so in early September after our day at Witheridge and took a rainbow which came home with me for my supper. That fish was one of two or three that appeared to be feeding at the surface and it’s stomach contained partially digested insect life which I couldn’t further identify. I’m not sure whether the fact there was nothing identifiable was due to unsuccessful feeding or just that the insects were fragile, crushed and that their digestion continued in the stomach fluid between hooking and eating! There was certainly no fry or parr there.

    Jim Parrott | October 12, 2013 at 1:28 pm | Reply
  2. Thanks for taking the time to comment Jim and yes I recall those fish, I bet they tasted good! I have seen the same thing, a kind of black sludge. All year I have not found anything like caddis larvae or proper nymphs which need to be found or hunted but some fish definitely had “sludge”. This appeared to be tiny midges which are easily taken at the surface. But mainly it was sticks, stones & weed!

    Nick Hart | October 15, 2013 at 1:18 pm | Reply

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