Fisheries development works
Some aspects of fishery management, such as the construction of deflectors and weirs to improve angling and salmonid production can negatively affect lamprey populations. Stream restoration activities can include projects that facilitate fish passage (e.g. culverts and fish ladders), various types of habitat structures (e.g. large wood, weirs and boulders) or complete channel restoration. Fishery management for one particular group may adversely affect other fish and wildlife and their habitats. For example, action aimed at improving conditions for salmonids, e.g. dredging of silts containing young lamprey of infilling them with boulders to create deflectors, or the provision of fish passes only surmountable by salmonids may be detrimental to lampreys. Nonetheless, many restoration projects that benefit salmonids aimed at restoring natural stream functions and floodplain habitat will also benefit lampreys by providing diversity in habitats, substrates, off-channel habitats, cover, and good water quality. However, it is recommended that enhancing lamprey habitats i kept in mind during these works, and limited to outside the lamprey spawning season.
The River Restoration Centre in the UK has published a ‘Manual of River Restoration Techniques’ (RRC, 2002), which, although focussing on salmonid fish species, identify a range of significant measures for the improvement of fluvial geomorphology and ecological status. Many of the restoration measures set out, particularly measures to increase channel complexity along drained stretches of river, would be likely to directly adversely affect lamprey juvenile habitat during the construction / works period; however, with sensitive timing of works and proper translocation taking proper account of lamprey species requirements, all measures to improve the health of a watercourse as a whole would be of benefit to lamprey.