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 BalanceThe 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.