Conservation of the native white-clawed crayfish, Austropotamobius pallipes, in the uplands of mid-Wales

British native white-clawed crayfish, Austropotamobius pallipes, thrive in calcium rich freshwaters, but have declined dramatically in the last few decades due to competition with invasive species, disease, loss of habitat and pollution. This thesis examines the current status of Welsh A. pallipes populations, causes of decline, fine scale genetic structuring and rearing of A. pallipes in captivity for conservation purposes. A conservation action plan was also devised. Distribution and abundance have continued to decline on tributaries from the 1990s into the 2st century. In remaining populations, numbers of females and juveniles were low, indicating further declines are likely. A. pallipes were no longer found on the main Wye River, were present in low numbers at only two sites on the main Usk River, while just a single individual was found on the main River Banwy of the Upper Severn Catchment. However, populations in the River Edw, a Wye tributary, had recovered somewhat by 2004. Declines were attributed to siltation, from intensive livestock poaching and sheep dip pollution from the synthetic pyrethroid, cypermethrin. Both causes are exacerbated by steep landscape and heavy rains. The threat of crayfish plague and signal crayfish invasion remains in the Wye Catchment. Genetic structuring of populations was found at three levels. Genetic structuring within a stream was observed in the River Edw, due to isolation by distance and human interference. Genetic variability differed between streams of the upper half of the Wye Catchment, where individuals were divided into two genetically dissimilar groups, those from the Upper Wye and those from the Lower Wye, possibly as a result of differing habitat characteristics. At the third level, genetic variability differed between catchments. For example, individuals of the Itchen Catchment in Hampshire, southern England, were genetically dissimilar from others surveyed such as those of the Wye catchment in Wales and those from the River Aire in West Yorkshire. This genetic structuring is important and should be considered when carrying out restocking programs. Rearing A. pallipes in captivity was relatively successful due to a high protein, fresh diet of diatoms and zooplankton