Crayfish in Scotland

Gladman, Zara F. (2012) Crayfish in Scotland. PhD thesis, University of Glasgow.

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Unlike the rest of Britain, Scotland has no native crayfish species. There are, however, two introduced species: the white-clawed crayfish (Austropotamobius pallipes) has inhabited Loch Croispol in Sutherland and Whitemoss Reservoir in Renfrewshire for several decades. A. pallipes is endangered in its native range and Scottish stocks may constitute an important conservation resource in the future. The other crayfish species in Scotland, the North American signal crayfish (Pacifastacus leniusculus) was first recorded in the wild in 1995 and has spread rapidly to inhabit many river catchments and standing waters, where it is considered a serious threat to native biodiversity. The purpose of this thesis was to conduct research into the distribution, control and impact of non-native crayfish in Scotland, with a main focus on P. leniusculus.

A comparative field study on the River Clyde in southern-central Scotland was used to test the efficacy of different sampling methods for detecting P. leniusculus in shallow, flowing waters. A combination of kick-sampling and three-run electrofishing was shown to be the most effective method and assisted in the development of a crayfish detection protocol. This protocol has been applied by fishery trusts across Scotland to determine the fine-scale distribution of P. leniusculus in rivers. Results of a radio-tracking study in the River Clyde catchment showed that P. leniusculus moves up to 195 m day -1 in lotic habitats, with flow and in-stream barriers identified as potential impediments to movement.

In addition to studies of P. leniusculus, surveys were undertaken to assess the status of the two A. pallipes populations in Scotland. Results showed the occurrence of a low density and high density population at Loch Croispol and Whitemoss Reservoir respectively. These sites could serve as long-term “ex-situ” ark sites for A. pallipes but only if measures are taken to mitigate the current biosecurity threats of P. leniusculus and disease.

Laboratory studies were used to assess the potential threat of P. leniusculus to Atlantic salmon (Salmo salar) redds and the globally endangered freshwater pearl mussel (Margaritifera margaritifera). The burial of Salmo salar eggs in redds appears to afford protection from predation by P. leniusculus but other life stages may be at greater risk. Crayfish attempted to predate upon M. margaritifera but were unsuccessful, probably due to the thick, protective shell of the adult mussels tested; predation of juvenile mussels is predicted to be more likely.

Finally, the impact of a large-scale trapping programme on a population of P. leniusculus in a large lake was evaluated using mark and recapture methods at Loch Ken in southern Scotland. The programme significantly reduced the number of males in the population but its effect on females was complicated by seasonal variation in trappability and the bias of traps towards males. Depth was found to be a significant determinant of the catch of P. leniusculus. Animals were also found to make significant movements of 800 metres in two weeks. Crayfish occur in Loch Ken at densities which are high compared with other lakes and the loss of native biodiversity there is expected to be considerable.

Continued research into invasive species such as P. leniusculus will provide valuable data to support management decisions and help tackle what is one of the top five drivers of human-induced global change.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: North American signal crayfish, invasive species, aquatic, rivers, freshwater ecology, lakes, crustaceans, non-native, exotic, Scotland, Clyde, Atlantic salmon, freshwater pearl mussels, white-clawed crayfish, Pacifastacus leniusculus
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > Q Science (General)
Q Science > QL Zoology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
Supervisor's Name: Adams, Prof. Colin E.
Date of Award: 2012
Depositing User: Miss Zara F Gladman
Unique ID: glathesis:2012-3977
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 01 Mar 2013 09:32
Last Modified: 01 Mar 2013 09:49

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