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Transforming a Research Concept into Commercial Practice: Addressing the ‘Hurdles’ of Single-Species eDNA-based DetectionThe use of environmental DNA (eDNA) for measuring and monitoring biodiversity has been identified as a novel molecular based method to complement more commonly utilised traditional ecological sampling techniques. It is a time and cost-efficient technique, which is rapidly advancing due to the capabilities of low eDNA detection levels. As the efficiency of the technique has increased, commercial organisations and end-users have gained a greater interest in its application. Despite this, the technique is currently only commercially available from a select few service providers. In the UK, the main target species for commercial scale eDNA-based detection is the great crested newt (Triturus cristatus). Interest has now been sparked for the development of eDNA assays to detect various other species, both for use as a regulated informative tool and a conservation aid. However, many recent studies have highlighted various limitations associated with the use of eDNA-based detection and this appears to be hampering commercialisation of this tool. eDNA-based detection methods remain relatively underdeveloped and un-validated for use as reliable and accurate widespread monitoring programs and other such applications. Here, the so called ‘hurdles’ associated with the development and validation of eDNA-based methods and its use as a fully available commercial service are reviewed and addressed, in order to develop and validate a commercially applicable eDNA assay for the endangered white-clawed crayfish, Austropotamobius pallipes, as a target organism. When designing novel species-specific assays, detailed validation steps need to be undertaken, ensuring they perform under various conditions, habitats, and which sampling methods should be utilised. Currently, more traditional methods used to asses populations of white-clawed crayfish (such as trapping and hand searching) are becoming increasingly more difficult to undertake as the species become rarer and populations more fragmented. Such techniques are therefore expensive (with regard to time spent surveying) and often result in low probability of detection. A new species-specific qPCR assay to detect white-clawed crayfish was developed and tested under various conditions both ex-situ (laboratory and mesocosms) and in-situ (ponds and rivers) to explore the optimum sampling strategy giving the most reliable results. Experiments were also conducted on a wider scale to determine the impact of DNA degradation and seasonal influence on eDNA persistence. Interestingly, this thesis illustrates that sample collection choice is not simple, and the ‘best’ methodology was shown to vary between habitat type. This indicates that great care should be taken when designing any such assays and implementing them in the field. Furthermore, this study highlights that a ‘standard operating procedure’ for eDNA-based detection in the commercial sector may not be possible and this will have to be explored on an assay by assay basis. Alongside case studies from real-world application of the technique, recommendations are made on how this novel eDNA assay can be used for the commercial practice of white-clawed crayfish assessment.