Habitat Restoration For Wild Brown Trout
It is now necessary to remedy these problems through river and stream restoration. River restoration should be approached in two ways. The first is to protect and manage existing good quality habitat, the second is to restore damaged areas where ever possible. Restoration is likely to cost more than protection as labour, machinery and the use of chemicals such as limestone are expensive. Also restoration may involve large scale operations. Care must be taken to prevent any "disasters" occurring such as diverting the flow and placing foundations or agricultural land under threat. Also many old mineworks could be made potentially dangerous or cause pockets of mine waste (slag etc.) Draining into the stream which can contain large lead and aluminium deposits polluting the water.
However it has been found that it is worthwhile enhancing even short lengths of river as very substantial fisheries and conservation improvements often accrue .
Although river restoration can have almost immediate effects good management is necessary to preserve the trout habitat once restored. It is necessary to note that a number of problems can be prevented and no cure would be necessariay. Therefore the management options described within this chapter can also be used as a preventative measure.
6.1 Reducing Harmful Acidification.
Soil hydrology is an important influence on stream acidity and aluminium concentrations
Experiments have been carried out on acidification in upland Ireland and the experiments (carried out by Brown 1990) have reached a number of conclusions in restoring trout habitat affected by acidification. Many sources of streams are within upland wetlands. These are areas of unimproved deep peat with little agricultural value, and often are covered by forestry plantations. One experiment was to see if liming such areas could reduce the acidity of a stream which source was within the peat (a feeder stream to the Erne). Two different limestones were applied to two different sites. Magnesium limestone and finely powdered calcium carbonate (Minfil 50). The surface water chemistry changes significantly following lime applications, however no change was recorded below 20 centimetres. This questions whether liming the actual site of the stream source rather than the actual point at which the stream starts is a viable option as the streams form within the peat, however surface run off does enter the streams so liming the source area should not be discredited. Changes in the upper peat water chemistry include an increase in PH, calcium, magnesium and oxidised nitrogen concentrations. The limestone Minfil 50 was found to be the most effective in raising PH. Alkanility and calcium concentrations. Liming peat does however, affect the vegetation. Liverworts such as Calypogeia muellereana and Cephaloziella spp. Sphagnums also reduced in numbers. So liming peat does have some environmental impacts upon the vegetation.
The experiments were then continued upon watercourses. Fish densities are known to be limited by habitat physiography. In order to understand whether such limitations would effect the results Cambell and Lendrum (1990) investigated habitat use by brown trout. The fish populations in ten continuous 10 metre reaches were assessed by electro fishing in six streams in Connemara. They contained only brown trout. So the presence of the fish was confirmed.
The streams represented excellent brown trout habitat, although the population densities were well below carrying capacity. Thus the streams in the Connemara area were probably limited by acidity and not habitat
Therefore a three year liming experiment was carried out (1987-1990). The three year period would allow for any juvenile trout to reach a substantial size close to maturity. The experiment was to see if liming was an effective measure to reduce acidity in trout streams. The results were very encouraging. Densities were significantly higher in post - rather than pre - liming years. Even lower stretches that were previously unfished now showed the presence of trout. The beneficial effects of liming for trout populations were also indicated by high survival in the field experiments within early life stages. Therefore it has been proved by liming the upper stretches (as close to the source as possible) brown trout survival has improved in limed streams. It can be stated that source area liming works well in buffering stream acidity and reducing aluminium concentrations.
The effect of liming upon wetland ecosystems are the subject of current research, however from the point of an environmentalist, a rise in brown trout numbers must mean that there is sufficient food to support this increase, i.e and increase in aquatic invertebrate.
There is concern that liming may create potentially toxic changes in aluminium speciatation in zones where limed and acidic aluminium rich waters mix. To assess this possibility a field experiment was performed (somewhat controversially) on one of Llyn Briannes feeder streams. The stream was dosed with powdered lime, an acidic tributary entered the stream 200 metres below the dosing point, and chemical and fish monitoring points extended up to 100 metres below the confluence. After 24 hours, brown trout mortality was 100% above the liming point, falling to zero within 100 metres downstream. There was also 70% mortality 15 metres below the confluence, despite little change in pH of total aluminium, mortalities were significantly correlated with concentrations of aluminium and iron in gill tissues. The results of the experiment carried out suggests that aluminium could occur where waters of differing acidity mix.
However the experiment fails to note the water level. If the stream was in flood conditions it would be unlikely to contribute towards any trout mortality due to the lime being quickly dispersed. It was likely that this experiment was carried out when the stream was at a low flow so dispersion would be more concentrated. Also the lower the flow the more difficult it is for trout to move from one pool to another, so they were in effect "trapped" within certain stretches.
6.2 The Use Of Buffer Zones In Protecting Trout Habitat.
Where possible, landowners are encouraged to leave strips of uncultivated land at least 10 metres wide alongside watercourses to develop as buffer zones. These permanently vegetated areas of land buffer the river against the physical and chemical effects of agriculture. Now, on many rivers, ploughing and intensive grazing takes place up to the rivers edge and soil, fertilizers and pesticides are swept into the water. The buffer zones also increase the ecological value of stream sides for many other species. The strips of land once removed from agriculture revert to a semi natural plant community can improve water quality and reduce silt inputs within the river. Buffer zones need to extend over the whole catchment, including small tributaries if they are to prevent silting completely, so they are not something which the local fishery manager can implement individually. Complete buffering is something which should be aimed for in the long term.
However recent research has shown that at least 50 metre zones of grassland is required to have a significant impact on the concentration of nitrates and phosphates reaching watercourses in agricultural land. It is believed that this is due to the fact that the root zones of wildflowers and grass species occupies only a shallow layer within 20 centimetres of the land surface, whereas many of these watercourses have a water level 1-2 metres below bank top during dry weather conditions which is when they are at their most vulnerable.
Therefore to increase the effectiveness of buffer zones it is necessary to include deep rooted trees and scrubs. These can also help to strengthen the bank and prevent erosion. Commonly used species are traditional broad leaved species such as Willow, Alder and hazel. Coniferous plantations are not used as buffer zones as the trees can increase acidification and surface run off due to the lack of forest floor vegetation. Forestry buffer zones are now recognised as an effective method of reducing agrochemical leaching. Obviously these take many years to grow and reach an effective age and are not viable for many agricultural situations due to the loss of cropland or pasture. However they can be implemented on upland stretches, particularly in Wales and Ireland where the stream side is already colonised by coniferous afforestation. The Buffer zone (both uncultivated and forest strips) will improve the habitat for trout through creating cover from overhanging vegetation, and also increase the feeding value for the trout from wind blown invertebrate onto the water from the vegetation.
As stated earlier stock access to water courses has a detrimental effect. Therefore to prevent this fencing should be placed at least one metre from the river bank. The fencing must be stock proof. All timber used should be treated softwood. Posts should be at least 80 mm in diameter, spaced 3 metres apart, and strained at 50 metre intervals or at changes of direction. When stock are not present, a nominal fence is still worthwhile to prevent accidental damage. Where cattle graze, the fence should have 3 strands of barbed wire, this should be augmented with wire netting if sheep are present.
The reason the fence should be at least 1 metre from the bank is to prevent stock from grazing the other side of the fence and damaging marginal plants. The fence will allow vegetation to grow. This in turn will result in the consolidation of the bank and ultimately in a narrowing of the stream. The value of excluding livestock from fisheries terms cannot be over-stressed enough. Environment Agency consent may be needed for some fencing operations as public access could be compromised.
6.3 The Management Of Marginal Plants Along The River And Stream Bank.
Once the riverbank is fenced off a dense sward of plants along the waters edge should grow. Species desired to offer cover for fish in upland Ireland include coarse grasses such as jointed rush Juncus articulatus, bulbous rush Juncus bulbous anc common sedge Carex nigra.
It is also beneficial if the plants and shrubs become partly submerged as this offers excellent cover for juvenile trout from predators. The marginal plants help to strengthen the bank and prevent erosion, they also assist in narrowing the channel to maintain depth and current speed. The marginal plants also provide habitat for a number of different species such as invertebrates, birds and aquatic mammals. This habitat will not flourish if stock have access so fencing is necessary. Constant management is important to prevent invasive plants or trees causing problems. Many landowners cut the marginal plants in the summer to allow access for anglers. This is not recommended as the banks offer refuge for trout and other wildlife during what can be a stressful period of the year, especially in low conditions. Marginal plants are an important source of food for trout as many wind blown invertebrate come from these areas.Little to no vegetation is found within the streams of upland Ireland so clogging up of spawning sites is not a problem. And no real management steps are needed. However vegetation cover can be a problem as stated earlier from trees and the next sections shows how effective management should be carried out.
6.4 The Management Of Riverside Trees To Improve Trout Habitat.
Bankside trees such as alder and willows have both good and bad points. The shade created as mentioned previously can damage aquatic ecosystems. However their roots are very effective in binding banks and preventing erosion. Also the roots provide excellent trout cover. Therefore the solution to these problems is to coppice the trees. This leaves the roots to bind the bank and shading is eliminated. Lower branches should be left and trained onto the water as this provides excellent cover for trout. Coppicing prolongs life of the trees and prevents areas of bank being ripped out by storm or flood damaged trees.