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Title: Invasion of the signal crayfish, Pacifastacus leniusculus, in England : implications for the conservation of the white-clawed crayfish, Austropotamobius pallipes
Author: Chadwick, Daniel David Adrian
ISNI:       0000 0004 7965 0734
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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Abstract:
The spread of invasive species is a key driver of UK native biodiversity loss. The UK's native white-clawed crayfish, Austropotamobius pallipes, is in severe decline. The primary contemporary cause of this decline is the invasive non-native signal crayfish, Pacifastacus leniusculus, and associated 'crayfish plague' Aphanomyces astaci. In this thesis, I provide an updated distribution map of crayfish in England. This work shows that A. pallipes continues to significantly decline within England, whilst P. leniusculus continues to spread. Special Areas of Conservation were also analysed in the context of localised threats. At a regional scale, I explored the impacts of P. leniusculus on native ecological communities in headwaters, using both A. pallipes and crayfish-free rivers as controls. At the highest observed Catch-Per-Unit-Effort, populations of P. leniusculus severely depleted both invertebrate abundance and richness. I considered P. leniusculus population density and structure to be paramount in understanding its invasion ecology, but the literature was often based on biased sampling methods or semi-quantitative data. A novel technique, referred to as a 'triple drawdown', was developed and tested along a high density invaded river, with the intention of defining an exhaustive method of surveying P. leniusculus. Densities in excess of 110 m-2 crayfish dominated by young-of-year and juvenile cohorts were recorded. The conservation significance of these findings are considered. Finally, the impact of dense P. leniusculus populations was explored, using Gut Contents Analysis (GCA) and Stable Isotope Analysis (SIA). P. leniusculus exhibited high levels of cannibalism in both low and high density sites. Both SIA and GCA showed a diversification to include other invertebrate groups under high density pressure. As a whole, the thesis shows the importance of understanding the fundamental information of distribution, structure and density of P. leniusculus populations, when attempting to manage this highly damaging invasive species, and conserve A. pallipes.
Supervisor: Sayer, C. ; Axmacher, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.779377  DOI: Not available
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