Fish in Loch Rannoch.
Perhaps the most famous fish in Loch Rannoch is the Charr (Salvelinus alpinus) which is now known to exist in three forms called morphs. Two of these live on the bottom of the loch (benthic) and one lives at the surface (pelagic). In their early lives the two benthic morphs both feed on invertebrates such as caddis fly larvae and freshwater shrimps. One of the morphs switches to eating fish (becomes piscivorus) later in its life. As a result this morph grows bigger. The surface living pelagic morph feeds on the tiny plankton floating throughout the loch.
Charr are found in a number of Scottish Lochs, in lake Windermere, and in tarns in Wales. In places they have been isolated since the ice ages and so have started to evolve into different forms. In Scandinavia there are forms that can live in both salt water and freshwater. In appearance they are rather like small trout.
Brown Trout are common in the loch and are the main species sought by fishermen. For many years the loch was stocked with trout reared in Yorkshire until it was realised that this was not a good idea as they would be genetically different from the native Loch Rannoch trout. Some of the older trout start to feed on other fish and become very large. These large trout are known as Ferox trout. They have large hooked jaws and generally look rather ugly. There have been some very big ones caught in Loch Rannoch over the years.
Rainbow trout have also been introduced into the loch but it is said that they do not breed here and so they may now have died out.
Before hydroelectric dams were built Loch Rannoch would have been a regular spawning ground for Salmon. There has been a huge decline in Salmon returning to the loch, perhaps because the fish ladders were not well designed. The fisheries research laboratory at Pitlochry has undertaken a project to try to return Salmon to the loch by seeding the burns around the loch with Salmon parr. Parr are an early stage in the life cycle of the Salmon. The researchers conduct electro fishing (stunning the fish with an electric current) every now and then to try to gauge the success of their efforts. The fish are not harmed by the electro fishing.
At the west end of loch Rannoch there are lots of Pike in the shallow reedy areas. The Pike is beautifully streamlined and is a voracious hunter which undoubtedly eats plenty of Trout and Charr. In days gone by the Loch Rannoch Hotel fished for these Pike and sold them in the restaurant as a delicacy. They are a very boney fish and so need careful cooking and no doubt careful eating.
In addition the loch contains populations of Perch,Eels and Three Spined Sticklebacks.
The Perch is a deep bodied fish with defensive spines associated with its dorsal fin that it can raise to deter a predator. Eels have a remarkable life cycle in that they breed in the Sargasso Sea and the young eels (elvers) make their way across the Atlantic to Europe and the up the rivers to bodies of fresh water such as Loch Rannoch where they grow to maturity. If necessary elvers can cross land to reach isolated bodies of water.
The Stickleback is a small fish which has a complex spawning dance. The male makes a tubular nest and does a zig zag dance to lure the female into the nest to lay her eggs. It is then the male who looks after the eggs and fry and fans them with his tale to ensure that they get enough oxygen. This behaviour was studied by the famous ethnologist, Niko Tinbergen who was himself a student of the so called father of ethology, Konrad Lorenz.
Loch Rannoch is what is known as an oligotrophic loch which means that it is low in nutrients. In other words it is not polluted by sewage or agricultural fertilisers. This is the way that we need to keep it.