The maintenance of trout and salmon spawning streams.
Each year Inland Fisheries Ireland staff carry out maintenance work on a number salmon and trout spawning channels. Most natural watercourses are self-maintaining and do not need any help. However, some rivers have been impacted in the past by human activity or invasive species and need intervention to ensure that they function in a balanced way for fish and the wide variety of natural life. Intervention takes place by Inland Fisheries Ireland through the following stream maintenance activities:
Maintenance of Spawning Gravel and Riffle Areas
Many river and streams rise and flow through calcium rich limestone ground. This environment supports complex aquatic ecosystems with a rich diversity of invertebrate life which is an excellent food source for salmon and trout. Over time this calcium deposits from the limestone and fine silt can settle on the riffle areas of the riverbed solidifying spawning gravels. In addition the subsequent growth of aquatic weed on the riffle and spawning areas can render the natural gravels unusable for salmonid spawning. This problem reduces the productivity of the river to recruit fish creating an imbalance in the life of the river.
Rivers and streams where this is prone to occurring are known by staff and targeted in a phased process, the gravel and weed is raked to break the layer of calcium and loosen the gravels necessary for spawning. Gravel may be introduced from time to time to supplement the existing spawning area where gravels have depleted.
Maintenance of Riparian Vegetation
Our riparian areas are naturally colonised by a mixture of trees, shrubs and plants. In some river catchments, this natural bankside vegetation has been removed for the promotion of agricultural or urban development. This encourages excessive sunlight to be penetrated to the riverbed, impacting on water temperatures, increased predation, instream weed growth and increased nutrients in the water column. In other places, long stretches of river can become dominated by excessive shading from trees and vegetation and this impacts negatively on biota within and outside the channel and the structure of the river itself.
There is a balance of shading to be maintained as rivers need trees and vegetation particularly with increased temperatures due to climate change. Staff maintain and enhance riparian vegetation through selective pruning, pollarding and coppicing. Where planting is required native species are used but natural regeneration and dispersal of species is encouraged and stock proof fencing is erected.
Invasive plant species can compete successfully against our native flora for space on the riverbank causing increased siltation, reduction in terrestrial biota and degradation of the habitat. Invasive plant species are removed by staff where possible.
Prior to any works being carried out, the rivers are subjected to an Appropriate Assessment process to ensure that no damage will be done to any vulnerable species or habitats connected to the project area. Inland Fisheries Staff carry out their maintenance projects while working closely with other wildlife conservation professionals to ensure that their work benefits all natural species that depend on our river and lake habitats.