An extensive study on the River Spey has demonstrated that the hatchery made an annual contribution to the rod catch of between zero and 1.8% in any given year. When account is taken of the fact that adult fish have to be removed from the wild to generate eggs and subsequently juveniles and that these fish would probably have spawned in any case, then any apparent minor “benefit” of the hatchery may well be outweighed by the reduction in natural spawning and juvenile production with survival rates for the latter likely to be higher than those achieved by hatchery reared fish.
Apart from the removal of fish which would otherwise have spawned naturally, other negative impacts include restocking eggs and fry in places where the adults would not have naturally spawned, and issues associated with the mixing up of different fish from different parts of a system which can dilute or change natural population structures.
Roger Brook, RAFTS Board member, commented: “Fishery Boards which stock salmon rivers for enhancement purposes need to ask some searching questions. Can they show definitively that their stocking is beneficial? Have they considered the impact their intervention will have on natural spawning? Furthermore hatcheries divert resources and manpower that could be more usefully employed in tackling other issues that are much more likely to increase stocks including removing man-made physical barriers to fish migration, restoring habitat and reducing human exploitation”.
RAFTS’ “general presumption against stocking of salmon” applies except in very specific circumstances, such as where there has been significant habitat loss or there are insurmountable challenges. Thus, in contrast to enhancement stocking, the RAFTS review acknowledges that “mitigation stocking” (to compensate for lost production due to a man-made scheme, such as a hydro-power dam, or activity that cannot be prevented or removed) or “restoration stocking” (for example where a population has been lost) may well be appropriate within defined parameters.