Otters, mink, fish, herons, cormorants; the trout’s early life is perilous. Many of a trout’s predators arrive from the air so overhanging trees and bushes will always provide a degree of safety. Once that little fish takes the plunge and joins the main river it’s life is constantly in danger and shelter from predators is essential. Often trout will have a bolt hole where they will flee at the first sign of danger. Many times I have poked my head too far over the bank trying to observe the feeding fish in a pool only to see the wake of fleeing fish heading for the safety of a root or overhang!
Shelter from the current
Trout will have to learn pretty quickly to put on weight, it’s vital that the energy they obtain from a food source is greater than the energy they expend whilst obtaining it. In faster currents the thousands of gnats & midges swarming over the water may be completely ignored with fish only rising to larger mouthfuls. Often the fishes lie in a feeding station just adjacent to a rock or maybe in a little depression in the river bed that provides some shelter from the current, nipping out from their lie to intercept a piece of food from the drift before diving back down to the same lie to wait for the next meal. Trout will live in unbelievably fast riffles and currents, so always fish those fast bits as you walk through them! Remember some trout (especially the bigger ones) may only rise to feed occasionally during exceptional hatches of flies so nothing rising does not mean nothing feeding.
In order to maintain and increase their bodyweight, trout will need a good food supply. As many flies and insects are seasonal, a diverse range of food is required so food is available all year round. The decline in river fly populations is a real worry however terrestrial insects will play a major part in the trout’s diet and fish often feed on the beetles, caterpillars and terrestrial flies that find their way on to the water. Waters where there are large population of freshwater shrimp will sometimes hold a good number of reasonable size fish, get turning a few of the rocks over in your stream to find out what the trout are feeding on!
River trout are fussy spawners requiring silt free gravel of between 0.5 and 5 cm diameter with quick clean water. They will spawn in the cool waters of winter when the saturated oxygen levels can be higher. It is believed that around 95% of trout die before they reach their 1st birthday so the better spawning habitats mean more fish will grown on to become a catchable size. Improving spawning habitats and reducing stocking is now commonly seen as a viable river management technique on many waters in the UK.
Trout thrive in well oxygenated water and require more oxygen than coarse fish so often the upper reaches of the river where the stream is turbulent and well oxygenated will contain a larger population of trout that will gradually thin out as the lowland river slows and becomes wide and silty.