Fishing The Fly Scotland Forum

Rob Brownfield

Re: Migratory browns....
« Reply #15 on: 07/01/2015 at 09:14 »
Firstly I have to state once more that the illegal stocking of any species is wrong, both morally and legally.

Secondly I am not going to enter into a pro pike argument, contrary to popular belief, I do not believe that Pike should be stocked into wild waters and I do not believe Pike have preference over other species.

On the issue of biomass, there is more than enough research, evidence and proof that nature controls its own biomass and the only time if suffers is when man interferes or a natural disaster occurs.

On the issue of "why not stock grayling into the Don, Devron etc"...cast your mind back 10 years...Grayling were seen as vermin, killed by the salmon guys. In fact, it still goes on on some waters. However, Grayling would directly compete for food with other salmonoids and there is even some evidence to suggest they predate on Salmon eggs. BUT, they would find a natural balance is allowed to.

One last thought...The Dee, Don, Isla, Tay, Tummel, Spey and so on all have Pike swimming in them. Are they plagued with Pike that eat all the trout and salmon? No, because the active "management" of Pike does not take place these days (at least on no real scale). They have been allowed to reach a natural balance and certainly on the Tummel, Don and Isla the wild trout fishing is superb.

Again, I will state that the illegal stocking of any water with any species is wrong! I would also like to add that the "selflishness, greed and ignorance" of those that LEGALLY introduce Rainbow Trout into waters where they did not exist before "can" be just as damaging.

Hamish Young

Re: Migratory browns....
« Reply #16 on: 07/01/2015 at 10:14 »
Aberdeen Uni did some radio tagging of Trout on the Don in the 90's.

This is interesting Rob, I hadn't heard of that before. Do any of the forum members know anyone who was involved with the project ??? I don't recall Jim Snr or Jnr mentioning it to me at any time, anyone else :z8 It's an absolute shame that important pieces of work which have been done in the past are often overlooked or forgotten about today, we should do better than that.

Could be some useful information in there at Aberdeen Uni tucked away in a darkened room or in the cupboard marked 'beware of the leopard' :z7

Back to the topic at hand, it would be of interest to me to see just exactly how many big broonies appear in the tributaries of the Don on/off during the season. Thinks.....  :z17

H :cool:


Rob Brownfield

Re: Migratory browns....
« Reply #17 on: 07/01/2015 at 11:04 »
Do any of the forum members know anyone who was involved with the project ???

I have been desperately trying to remember the chaps name! He later moved down south and did tagging for Barbel for the EA and was featured in Anglers Mail. I even remember seeing an online piece on him as he was making some interesting discoveries.

Leave it with me, I will dig through my emails...

There are online published results regarding Lochs Kinord and Davan done about the same time....if you can find them they might give you a contact name as he was involved with that to...as a student.


Mike Barrio

Re: Migratory browns....
« Reply #18 on: 07/01/2015 at 11:12 »
Was it Brian Shields? ..... Seems to ring a bell :z8

Rob Brownfield

Re: Migratory browns....
« Reply #19 on: 07/01/2015 at 12:22 »
Was it Brian Shields? ..... Seems to ring a bell :z8

Not a name I recognize.....

However, the Aberdeen Uni survey of Kinord and Davan is listed as being done by Treasurer, Owen and Bowers, 1992. That might be a starter for ten if anyone has access to the Uni archives?

Rob Brownfield

Re: Migratory browns....
« Reply #20 on: 07/01/2015 at 12:25 »
Just found some information on a study conducted on the Don in 1984 by "Mann, Mills and Crisp".

Interestingly this contains the only evidence I have found of Gudgeon on the Don, with an age range of 1-6 years in the samples caught. I bet a few Trout have grown big on these!

Allan Liddle

Re: Migratory browns....
« Reply #21 on: 07/01/2015 at 13:01 »


Back to the topic at hand, it would be of interest to me to see just exactly how many big broonies appear in the tributaries of the Don on/off during the season. Thinks.....  :z17

H :cool:

Even more interesting if they can show if these trout are 100% fresh water resident fish or have spent a bit of time in the salt?

Allan Liddle

Re: Migratory browns....
« Reply #22 on: 07/01/2015 at 13:12 »
Firstly I have to state once more that the illegal stocking of any species is wrong, both morally and legally.

Secondly I am not going to enter into a pro pike argument, contrary to popular belief, I do not believe that Pike should be stocked into wild waters and I do not believe Pike have preference over other species.

On the issue of biomass, there is more than enough research, evidence and proof that nature controls its own biomass and the only time if suffers is when man interferes or a natural disaster occurs.

On the issue of "why not stock grayling into the Don, Devron etc"...cast your mind back 10 years...Grayling were seen as vermin, killed by the salmon guys. In fact, it still goes on on some waters. However, Grayling would directly compete for food with other salmonoids and there is even some evidence to suggest they predate on Salmon eggs. BUT, they would find a natural balance is allowed to.

One last thought...The Dee, Don, Isla, Tay, Tummel, Spey and so on all have Pike swimming in them. Are they plagued with Pike that eat all the trout and salmon? No, because the active "management" of Pike does not take place these days (at least on no real scale). They have been allowed to reach a natural balance and certainly on the Tummel, Don and Isla the wild trout fishing is superb.

Again, I will state that the illegal stocking of any water with any species is wrong! I would also like to add that the "selflishness, greed and ignorance" of those that LEGALLY introduce Rainbow Trout into waters where they did not exist before "can" be just as damaging.

Please don't think my previous reply was meant to provoke, merely tying to point out what's happened elsewhere, however in the interest of no hijacking a really interesting thread i'll simply end with this.
Agree on you reference to illegally stocked fish Rob especially when there is a danger that they might be fished for using other fish wich themselves may then be released into the given water.

Grayling were until recenty regarded as vermin widespread through the lower half of Scotland, thankfully a position that for the most part has changed and looks to continue that way.  Sadly there are areas up here where our browns are regarded as vermin i'm afraid and will be / are removed given half a chance.

Finally the upper Spey does indeed hold pike (which i'm informed were intriduced late 60's?) and where the conditions suit have decimated the resident trout populations as well as have had an impact on migratory fish (especially migrating smolts).  Agree that nature will find a balance but where conditions are favourable the balance will be 90% pike, 10% trout or thereabouts.

Anyway lets get back to the topic at hand migratory browns.
I'll ask the Moray Firth Trout Initiative guys if they've anything from the Don taging project or know where we can possibly look for it.

Rob Brownfield

Re: Migratory browns....
« Reply #23 on: 07/01/2015 at 14:16 »
Agree that nature will find a balance but where conditions are favourable the balance will be 90% pike, 10% trout or thereabouts.

I am really sorry, but those figures are not supported by the scientific findings. There have been extensive studies done on this all over the Northern hemisphere, and without fail, the predator always remained in the minority.

Please review the extract below from a report produced by Dr. B. Broughton B.Sc. (Hons), Ph.D., F.I.F.M.
Prof. B. Rickards B.Sc., M.A., Ph.D., Sc.D, D.Sc, C.Geol., F.G.S., N. Fickling B.Sc. (Hons), M.Phil, I.F.M. Dip., D. Lumb B.A. (Hons) and C. Leibbrandt.

(Sorry for the large cut and past, but I only have a word document, no link to the report online...)


iv. Natural Balance
The data from numerous sources demonstrate that on stable fisheries there is a weight-to-weight
relationship between predatory fish and the prey which are available to them. This finding is in direct
agreement with the original assertion of Johnson (1949) and the detailed pond experiments conducted by
Swingle (1950). The studies on the status of the ponds, either balanced or unbalanced, revealed that the
predator/prey ratio, by weight, of balanced ponds was between 1:1.4 to 1:10. The studies showed that
77% of the best ‘balanced’ populations had ratios between 1:1.3 and 1:1.6.
Conversely ‘unbalanced’ populations had ratios of between 1:0.06 and 1:63. Most unbalanced populations
had a relatively small weight of predators in relation to the weight of prey. It appears that the weight of prey
present is a function of the fertility of the water, whereas the weight of predators is, within limits,
dependent on the weight of prey.
Since the results of these studies were published it has been confirmed that in most established fisheries in
Britain, the ratio, by weight, between pike and their prey is approximately 1:10. This has been determined
from the results of hundreds of counts of fish following the complete de-watering of fisheries or total fish
mortalities and the findings have been confirmed by fish population studies using seine nets, electro fishing,
traps etc.
In his review of a large quantity of data derived from eastern European predator fisheries, Popova (1967)
cites pike biomasses of 10-13 per cent of that of their available prey; Kell (1985) lists survey data for the
Sixteen Foot drain which give a relationship of 12 per cent; and Templeton (1995) recommends that pike
fisheries should be stocked with prey fish at a weight of eight times that of the pike. When Broughton
(unpublished data) analysed the catch statistics from several hundred scientific surveys of still and running
water fisheries in the English Midlands, an average weight ratio between pike and their available prey was
found to be approximately 1:10.
Using the ratio of 1:10, one can predict that 300lb of prey fish would be able to support some 30lb of pike
without any long-term, adverse effects on the abundance of either type of fish. A useful analogy is to imagine that the prey fish represent a sum of money which is invested. In effect, pike are consuming the
interest, leaving the capital sum untouched.
This balance is a so-called dynamic equilibrium - in other words, it will swing one way or another in
response to entirely natural phenomena (such as spawning success or outbreaks of disease). Equally, if
the balance swings markedly in favour of one 'side', ecological pressures ensure that eventually it will
swing back in the other direction (described in detail by Carlander 1958 and Anderson & Weithman 1978).
If this were not the case, there would be countless examples of fisheries in which pike have become
dominant or have totally eradicated the stocks of prey fish, and this would be a continuing situation on
unmanaged waters. We have reviewed a huge volume of the published scientific literature on pike in the
British Isles, Europe, North America and elsewhere, and there appears to be just one example where pike
had 'eaten themselves out of house and home' (Munro 1957).
Ricker (1952) described three types of numerical relationships between predatory fish and their prey. Mann
(1982), Kell (1985) and other authors have concluded that pike probably fall into Ricker's Type B model, in
which: "Predators at any given abundance take a fixed fraction of prey species present, as though there
were captures at random encounters". This means that predation is dependant on the numbers of prey,
rather than the numbers of predators.
Because of the annual production of fish flesh within a fishery as a result of spawning and growth, there is
little danger of pike consuming a large percentage of the potential prey fish. They will, in fact, consume some
of the surplus fish flesh produced each year, ensuring that the weight of both predators and prey remains
in balance.

Simon

Re: Migratory browns....
« Reply #24 on: 07/01/2015 at 15:37 »
What a super topic! I think Dryflee is right about this actually because while prey does indeed control predator in the case of pike it's not that simple because they are both prey and predator. I have read that the main food of large pike is small pike so it is perfectly possible for pike to almost eliminate all other species but still maintain a large population by feeding off each other.

Will Shaw

Re: Migratory browns....
« Reply #25 on: 07/01/2015 at 16:20 »
What a super topic! I think Dryflee is right about this actually because while prey does indeed control predator in the case of pike it's not that simple because they are both prey and predator. I have read that the main food of large pike is small pike so it is perfectly possible for pike to almost eliminate all other species but still maintain a large population by feeding off each other.

Happy to accept this Simon, but you'd need to site some studies supporting this. Saying "I've read that..." is fine but you need to provide references. All the studies Rob sites seem to contradict your statement.

More pertinent to the argument is whether there is any information about the impact of pike introductions on the balance of different prey species in a water. You could, for instance, maintain a constant biomass of prey species but within that see one prey species (initially) heavily predated and replaced with another?

Should say that, as with everyone else, I'm against any unofficial/illegal stocking of any species.

Allan Liddle

Re: Migratory browns....
« Reply #26 on: 07/01/2015 at 17:25 »
Ok you've pressed me into one final reply Rob; how do you explain the decemation of natural trout stocks on waters where they were once prolific as a direct result of pike introduction?  I don't mean a slight drop as per your 1:10 figures i mean the actual fact that trout are quite simply not there.
Accepting the possibility that these fish had altered feeding and behaviour patterns as a result of the sudden and increasing appearance of a highly efficient predator, but when looked at further waters such as Callatter (previously listed as similar trout population to Lochindorb and where estate thought it good practice to introduce pike in a bid to reduce trout numbers hence increasing size and quality of sport, noting also that this water isn't the only example you could site here) demostrate an almost total elimination of the previous residents.  However if you then check the feeding streams large enough to sustain trout populations, these are found to be healthy in terms of trout numbers (Loch Luichart) eleminating the possibility of other explanation for the trout demise in the loch.

Yup totally agree Will and you're correct (as Simon notes also) that it is possible for a water to have the original population of fish replaced by a predator who then maintain their existance by feeding on each other.  The evidence we have for this in terms of pike indicate that initially there were a few really large pike only for this to level out some time later into a much smaller but much more prolific average size (with obviously a few still in the Rod Bender range).  In essence exactly the same result as we've seen where trout have been introduced into 'virgin' waters and left to their own devices.

Guys i'm sorry but we have actual real practical examples covering a multitude of time ranges (Callatter being the earliest i know, Spey system more recent, Lochindorb probably the most recent of all) where we can clearly see the devastating effect on the trout population from pike introduction is all i'm saying.


Hamish Young

Re: Migratory browns....
« Reply #27 on: 07/01/2015 at 18:11 »
Even more interesting if they can show if these trout are 100% fresh water resident fish or have spent a bit of time in the salt?

You know my feelings on the subject.... if your memory is good think back to that day of 'trout' discussion on Watten a few years back :wink

H :cool:

Hamish Young

Re: Migratory browns....
« Reply #28 on: 07/01/2015 at 18:19 »
Guys i'm sorry but we have actual real practical examples covering a multitude of time ranges (Callatter being the earliest i know, Spey system more recent, Lochindorb probably the most recent of all) where we can clearly see the devastating effect on the trout population from pike introduction is all i'm saying.

Chaps I'm not aiming this at any one poster (I know Allan, I have quoted you but this is amied at all posters in this thread) but we stand a chance of diverging so far from the original topic as to make the thread title pointless. Can we please keep this thread about the vagaries of trout residence/migration and leave the Pike to themselves .....in another thread if required :?

I appreciate that there's interest and relevance, but let's keep it in another thread. I'd rather not moderate unless I must :!

Cheers  :z16

:wink

Allan Liddle

Re: Migratory browns....
« Reply #29 on: 08/01/2015 at 09:38 »
Yup sorry Hamish, if there's a feeling the pike discussion needs to continue (although i've said all i want to about it) then someone could simply start a new thread?

Anyway back to to the original subject, when were we on Watten??  :z4 :z4

I'll keep the rest of my powder dry until my wee script comes out hopefully next month or the one after.

 




Barrio Fly Lines - designed in Scotland - Cast with confidence all over the world

Barrio Fly Lines

Designed in Scotland

Manufactured in the UK

Cast with confidence all over the world

www.flylineshop.com