The Grayling affect.

[Glyn]

Hi all I have a question. I have been wondering about the affect Grayling have been having on the natural trout stocks to our East Wales rivers, I know there are great stocks of Grayling in these rivers and they are getting bigger this is obvious with all the catch reports stated here on this forum.

Now my understanding of this fish it travels around in shoals working and feeding up and down a bit of river untill it finds food and venturing further along the river until it finds food.

Please understand something here I am am not knocking this fish as on occasions I fish for them myself and enjoy the day out, but I am also concerned are these fish which are spreading very well and increasing in head of fish damaging the food supply to the natural brown trout in these rivers.

Steff I know you are very well versed with grayling and a couple of others here on this forum what is your take on this question, will they cause a problem for our trout in the future on these rivers ...as these rivers are not that big compared to the likes of the Severn and Tweed and food could be hard to find.
Cheers Glyn.

[tigermoth]

Hi Glyn
My experience of grayling and trout is that rivers can sustain healthy populations of both. You will find that the populations wax and wane in terms of numbers and size but this is more to do with the natural cycle of the species populations rather than their impact on each other.

The river system I fish most - the Monnow - has very healthy populations of both species. Whilst they do have some habitat requirements in common, you will also find that the fish have their own niche habitats which change across the season as the conditions of the river alter. Sometimes I will fish a stretch and catch only grayling and think to myself "Where have the trout gone" - other times on the same stretch, the reverse can be true.

Both are fine species and nature intended them to exist alongside one another - why f*ck about with it. Look at the rivers of Scandanavia - rammed with all species of salmonid.

[Diawlbach]

I think I'm right in saying that grayling were stocked in the Taff rather than being an indigenous population, they weren't around when I was young.

They appear to be far more successful than the trout, the increase in their numbers is staggering.
I suppose one could argue that the grayling are occupying a niche in the aquatic environment hitherto left vacant by the other species in the river but from my personal experience I'd say that was not the case.
When I fish a dry fly for trout in the early summer the grayling are back on form and I find it increasingly difficult to predict whether it will be a trout or a grayling that will take the fly.

Years ago it was rare to hook a grayling but now they are definitely competing very successfully for the artificial fly and by inference I would suggest that this is the case with the genuine article along with all the other food available in the river.

Coming back to your question Glyn I'd say that the grayling will have a detrimental effect on the number of trout in the Taff as I believe that they compete with them and appear to be the victors at the moment.

Whether this rapid increase in the population levels of grayling is purely an upward rise in a fluctuating pattern of growth is debatable, personally I think that the numbers will rise until the available food in the river begins to limit their expansion at which point the numbers will remain static unless the food supply should change.

Having said all that it should be recognised that the spread of grayling appears to be limited by the geography of the river, in the Taff and Rhymney there seem to be definite cut off points for the species but whether this is due to Nature or to unnatural barriers in the river is a question for the experts.

[Glyn]

Diawlbach I found what you have said interesting, I am of the same way of thinking to most of what you have said. Friends of mine fished Angling 2000 waters in Devon and Cornwall as I do, and they are finding it hard to get through to the trout because of the Grayling in certain very small rivers something like 4 to 1 ratio in favour of the Grayling.
I fished with them on one beat of the Inney I think last season for trout in June I caught more Grayling than trout that day.

I dont know what they breed like compared to trout but it seems to me ( I may be wrong) but they seem to have the upper hand.

Also as Tigermoth says on some of our rivers there does'nt seem to be a problem, but are these rivers stocked with browns yearly or is the head of trout natural. I know in the Scandanavian rivers which some are huge the two live quite happily together but maybe the food supply is greater I dont know.
cheers Glyn

[Teifi Terrorist]

Interesting one this. For the record, I'm from the 'Tigermoth' school of thought.

glyn said:

I know there are great stocks of Grayling in these rivers and they are getting bigger this is obvious with all the catch reports stated here on this forum.

I am also concerned are these fish which are spreading very well and increasing in head of fish damaging the food supply to the natural brown trout in these rivers.

I'm not sure about them getting bigger to be honest Glyn, I just think there's more people out fishing for them now, since they're becoming the 'in' species (more people fishing for them, and more people doing reports on them! The age old media scenario; people don't know what's going on in the World if it's not reported). The Severn, Wye, Dee will have a lesser amount of grayling, but larger specimens, or larger, nomadic grayling. The Taff, Rhymney etc. will have one hell of a lot more fish, but I think that, perhaps due to competition, you will not get the 50cm+ reported from the aforementioned rivers. I'm sure that there's one or two in the Taff, but in relative terms, nothing close to the other systems - in addition, I would be very surprised if a 45cm+ grayling came out of the Rhym. Again, I'm sure they're there, but certainly not in numbers.

As for the second point of competition with the trout; I certainly haven't found this to be the case. Grayling, by nature, tend to be a shoaling species - even in the summer months, they may not be as tightly packed as they are in the winter, but they are certainly to be expected in the same general area. Trout tend to have lies, or are more nomadic by nature. You will, at times, find them intermingled and competing for food, but I would say that the trout would be the victor at such times - it certainly is a faster and more agile species than the grayling.

Take the Taff, for example, it has an immense head of grayling, a population that seems to be increasing every season - I've fished it for 10 years, and I've certainly seen a change. However, EVERY trout that you catch, no matter of size or season, is in superb condition - beautifully fat, and in superb all-round form. The truth being that there is such a healthy level of natural food in the Taff that it will sustain both species admirably and without fail in its current condition. Perhaps other rivers with a lesser head-count have a lesser head-count because nature has met the equilibrium between food supply and sustainability?

In addition, I'm sure that the young grayling become a food source for the trout - perhaps we will have a strain akin to the marble trout evolve in years to come! ;D They eat grayling up to 35cm! or even larger in some instances, and they themselves grow to over 40lbs.

TT.

[Hoppy]

Bill,

I'll try to explain on a separate thread, however the Grayling Afficiandos TT & Daz will be better placed.

On the thread re Grayling i have a few thoughts.

Firstly i dont think they have an adverse effect on Trout numbers or size, i think they live quite happily hand in hand or fin by fin!!!

However, and this is totally based on thought rather than scientific study, i believe there may be a correlation between Grayling size and Salmon

The rivers TT mentions as producing large fish - the Severn, Dee, Wye - and add to that the Tweed system are all (or once were) reputed to be excellent Salmon Rivers.

I am pretty sure that Grayling move up and down river through the season perhaps in the search for food. And this is where i think that the connection with Salmon comes in.

Im sure that i have read that Grayling will sit behind redds and take loose eggs from hen fish. This is a good source of food and an excellent source of nurishment. Perhaps this explains the size of the fish on the aforementioned rivers. Grayling can get right into the area where fish cut redds.

Further to this, i wonder if the weirs on the Taff and Rhymney prevent Grayling reaching the redds? Im sure that some migratory fish will spawn further down stream, but perhaps the bigger numbers are in areas where the Grayling cant reach. However the Taff and Rhymney have good numbers of fish - and excellent fly life. Far better fly life than i have seen on the Dee or Severn.

The Severn is fairly open to Grayling all the way up and beyond Llanidloes, and the Dee is open all the way up. However there are Grayling in Bala.

It might be nothing but it might be worth considering.

I for one dont mind them, in fact its a pleasure to see them in the Winter.

But if you mention Barbel i'd have a different view. Id hate to see them in the Upper Severn or Upper Dee.

In fact im sure the demise of the Wye may have something to do with the introduction of these non native fish. I hope that Sewinbasher can comment on this as he knows the Wye and may be able to give his thoughts.

As for trout, i think they are safe.

Hoppy

[Glyn]

Having read the last few replies.. I can see what you Steff and Hopppy are saying and I agree to an extent, but if these fish are artifically intoduced into a smallish river system knowing full well that nature tries its best to keep a balance in the system.. surely double or trebbling ( more bad spelling )the head of fish in this river will cause a shortage of food for fish and including bird life that feed off olives hatched from nymphs.

The question you Hoppy has just raised about the grayling eating salmon eggs is a very good point I pressume they take trout eggs also and young fry too..you can catch grayling on small mepps so they are a predator. I wonder now since Hoppy has brought this up has the salmon rod catches dropped more so on rivers that hold grayling than rivers that do not ( I know salmon catches are down nationaly ).

Steff I hope we dont get 40lb trout my Drennan 3lb sub surface will have a fit ;D.
Glyn

[Teifi Terrorist]

glyn said:

The question you Hoppy has just raised about the grayling eating salmon eggs is a very good point I pressume they take trout eggs also and young fry too..you can catch grayling on small mepps so they are a predator. I wonder now since Hoppy has brought this up has the salmon rod catches dropped more so on rivers that hold grayling than rivers that do not ( I know salmon catches are down nationaly ).

Steff I hope we dont get 40lb trout my Drennan 3lb sub surface will have a fit ;D.
Glyn

Glyn, I reckon you may need to step-up to 5lbs, that should suffice! ;D

Grayling certainly to predate on fry - more than people think!

As for the numbers of fish doubling or trebling, I don't think this is or can be the case - basically returning to what I said previously about the rivers reaching a balance between food supply and fish sustainability. For example, the Wye, Dee, Severn have had grayling for decades, and those rivers have found their 'level', as has the Taff and Rhymney, which, largely due to food supply, no doubt, can support and sustain larger populations.

I'm sure that grayling would take loose salmon/trout etc. eggs, but I really don't think that they have the capabilities or power of e.g. barbel to forage deeply enough into the redds to actually 'kill off' and entire redd - if the salmon lay their eggs in sand or silt, which they don't, then there would be a case for the grayling being able to sift through it, but moving large quantities of gravel in search of caviar isn't plausible for the species in question. Again, barbel; now that's a different matter.

TT.

[ianw]

Personally I don't think that Grayling eat Salmon/Trout eggs.

The efficiency of those pink bugs is purely a coincidence

Best regards,

Ian