BEAULY SYSTEM FISH AND FISHERY ACTION PLAN ... - RAFTS

3. Factors Limiting Fish ProductionFish production within both the Beauly system is a function of natural factors suchas the availability of spawning and juvenile habitats and anthropogenicallyinduced factors such as the loss of smolts due to damage by hydro-electricturbines. For the purposes of this report, emphasis will be placed on anthropogenicfactors or factors in which anthropogenic intervention is likely to haveexacerbated natural constraints. The system has been subjected to considerableanthropogenic alteration, which is likely to have considerably lowered itsproductive potential. It is recognised, however, that many of the fish speciespresent are highly migratory in nature (e.g. salmon, trout and eels) and thereforefactors affecting the marine environment, both natural and anthropogenic, are alsoan important consideration in determining overall productivity.For the purposes of this report the following are considered to be the mostimportant potential limiting factors. Many of these factors have been identified bySEPA and have been discussed via the Area Advisory Group.I. Impoundment and Water Abstraction.The Beauly system has been subjected to extensive hydro-electric schemes. Thisis likely to have impacted upon its productive potential in a number of waysincluding lack of access for migratory fish to historical spawning areas due to lackof fish passes in some dams, provision of inefficient fish passes, alterations tohydrological regimes, changes in water chemistry and nutrient status, lack ofsediment transfer, the creation of ‘pinch points’ for the predation of bothmigrating juveniles and adults and the transfer of water between rivers which mayalter migration patterns. Other significant sources of impoundment and abstractionare also present on the Beauly system (e.g. by Scottish Water).II. PredationFish species are removed from the Beauly system by a suite of predators –including species introduced to the area (e.g. pike). For migratory speciespredation occurs in both freshwater and marine environments. Predation pressuresmay well be exacerbated by the presence of structures such as dams etc whichcreate ‘pinch points’. Of particular concern is predation on migratory fish duringstages of their life cycle after which density dependent compensation for losses islikely to be exhausted e.g. salmon and sea trout smolts and returning adults.III. Non-native species.The Beauly system contains a variety of species that are not native to theHighlands of Scotland. This may increase levels of predation (e.g. mink and pike)or increase competition for food and habitat (e.g. minnows).26