Zeolite.
I beg to differ about Freuchie...it used to be a very good, balanced fishery, with good trout fishing and good Pike..but thanks to the intervention of man, ie. the trout syndicate started to kill the bigger Pike, they ended up with a fishery full of small Pike. The Tayside Branch of the PAC went to advise them on the management and control of Pike, with a little success. When a Pike syndicate got hold of it, the balance started to be re-addressed and the trout started to show signs of improvement...but then the Pike guys lost the lease. This is a pattern that has happened time and time again and more enlightened fishery managers are starting to realise that Pike, when at the correct biomass, will enhance a fishery by keeping down the coarse fish and picking off injured or sick trout. This can be seen at waters like Rescobie, Menteith, Butterstone etc that have stopped netting Pike and have seen profits to be made from allowing pike fishing in the winter. Even the likes of Steve Parton, Bob Church, Roman Moser, Peter Cockwill, etc etc have fished for Pike on the fly in trout waters and see Pike as a valuable resource.
Its all to do with biomass of predator versus prey. There is lots of info on the web about it and i dont have the space to go into it
but if you are interested about Pike in trout waters and how they can improve rather than hinder the trout population have a look here.
http://www.pacgb.co.uk/pdfs/pikeinyourwaters.pdfWith Kinord, Aboyne and Skene the Pike population has been unbalanced by the use of set lines and illegal removal of fish. Many of the large fish have been killed and so we are seeing an explosion of tiny Pike that are not being controlled by the bigger females.
What one has to remember is that a large Pike is a lazy b#gger. It will rather scavange than chase and by and large, a healthy trout is way too quick and agile for a Pike. During the survays that have been done on Kinord and davan by the University its been shown that the most predated on species was the common eel, followed by Perch, then trout. However, a small pike is a typical kid in that it will grab at anything that looks edible and this can lead to damaged trout. So a water with lots of small pike is a bad thing, a water with big Pike is a good thing.