The Shannon, Ireland's largest river, is used for hydroelectricity generation since 1929. Subsequently, the Electricity Supply Board assumed responsibility for management of its eel stocks, due to the impact of the hydro-dam on recruitment to the commercial fishery. In order to negate a decline in juvenile recruitment resulting from the installation of hydroelectric facilities, management was focused on stocking lakes with elvers and fingerling eels. These were trapped at the hydropower facilities and in estuarine tributaries during their up-stream migrations. Due to the decline of natural recruitment in more recent times, attempts have also been made to develop an estuarine glass eel fishery. Stock levels are then monitored through annual surveys of the population trends of juvenile (glass eel, elver), growing phase (yellow eel) and downstream migrating pre-spawners (silver eels). Survey results and fishery management programmes are reviewed in this article. In addition to the long-term effects the hydroelectric facilities have had on the stock levels, there is also an annual effect on the migratory patterns of downstream migratory silver eels. In the lower reaches of the river system flow rates are regulated by the hydroelectric stations. We review previous work that had highlighted the importance of flow in determining the timing of the silver eels migrations, and assess the relationship between flow and migration in more detail through the use of hydroacoustic and telemetric studies. Current research on seaward migrating silver eel populations, suggests that spawner escapement rates can most effectively be increased by trapping migrating eels at fishing weirs located up-stream of the power station and transporting them towards the estuary.

The tolerance of incubating salmon embryos to spawning gravel sedimentation was examined under hatchery conditions and also in the natural state on the River Bush, County Antrim, Northern Ireland. In a laboratory assessment alevin survival was closely related to the level of fine material. The number of individuals was reduced at the 10% fines level while >15% fine material was found to be deleterious to survival. Mean survival on the river (19.26%) was found to be better than that recorded in the hatchery, although no clear relationship was established between the level of fines and percentage survival in the wild. The mean fines accumulation (13.59%) in the river incubators at the end of the experiment was shown to be statistically similar to the background substrate. The role of high flow events in the contamination of gravels scoured by spawning fish is discussed.

The European smelt Osmerus eperlanus L. is listed in the Irish Red Data Book as vulnerable. Known from only a few locations around Ireland, its distribution appears to be disjunct and all populations confined to estuarine habitats. The current paper gives an overview of the species' ecology, biology, status and known distribution in Ireland today, with emphasis on the resident population on the River Shannon from which they were first described in Ireland.

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Three survey techniques, a fully quantitative, multivariate study; a shorter or truncated fully quantitative method and a Geographical Information System (GIS) based, semi‐quantitative, survey technique, were developed to assess in‐river salmonid habitats on a catchment wide basis. These methods were tested and compared on three river systems in Northern Ireland: the Blackwater, the Bush and the Main. The research indicated that the fully quantitative method generated an accurate habitat database but required a high investment in time and resources to complete. The truncated survey approach often produced an inaccurate habitat database. The semi‐quantitative technique generated a more accurate habitat dataset with greater productivity and efficiency for the resources invested in the survey.