Bolstering the wild populations of white-clawed crayfish Austropotamobius pallipes, through captive breeding, rearing and release of juveniles into favourable in-situ habitats

Abstract

The white-clawed crayfish Austropotamobius pallipes, is a freshwater crustacean native to Europe and is endangered throughout its range due to habitat fragmentation, pollution, competition with the invasive American signal crayfish Pacifastacus leniusculus, and the associated disease, crayfish plague (Aphanomyces astaci). Production of captive-born A. pallipes for wild release into ark sites is a recognised conservation measure to help halt the decline of this species within the UK.
The aim of this thesis was to optimise aquaculture methodologies to maximise ex-situ production of A. pallipes, whilst exploring effective techniques to monitor released individuals, so that their activity patterns and long-term survival could be assessed. A series of hatchery experiments were conducted investigating stocking density, grading and dietary regimes for rearing juveniles. Key findings were that young-of-the-year A. pallipes can be reared at high densities (300/m2) without compromising survival; however, the optimal stocking density that maximised growth and health was 100/m2. Juveniles exhibit sexual dimorphism as early as six-months of age, and sex, rather than size, was the main factor that led to dominance hierarchies and growth suppression in juveniles. Maintaining juvenile A. pallipes in single-sex groups was optimal. Live food was optimal for high survival and growth in hatchlings, and a plankton diet produced increased growth in juveniles than a pellet diet.
Key findings for the tagging and tracking studies were that A. pallipes with a carapace length of 21 mm and above can be safely injected with passive integrated transponder (PIT) tags without survival or growth being compromised. Detection of PIT-tagged crayfish is limited to 150 mm, which is reduced to a 45 mm detection range when crayfish are within refuges. Long-term tracking using acoustic telemetry can provide useful data on activity patterns; A. pallipes are strongly nocturnal and are most active in spring and autumn. However, the methodology may be limited when used in still-water sites possibly due to interference from surfaces or other sound waves.
The findings from this thesis have influenced the aquaculture methodologies now used at the Bristol Zoological Society’s crayfish hatcheries. This has led to increased productivity and more wild releases, which are significantly contributing to the conservation effort for this species, helping to halt its decline in south west England.

Date of Award	26 Nov 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Grainne Mccabe (Supervisor), Gareth Jones (Supervisor) & Paul Stebbing (Supervisor)