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Nicky Green CEnv MCIEEM
Intro to invasive crayfish
Crayfish impacts
The Barle Project
Est. 650 species globally
540 million years
Occur naturally on all continents except Africa
Highest diversity = North America, 405 species
Five species native to Europe
Tasmanian Giant 7kg Eastern Swamp 2cm
Rob McCormack; CC-BY 4.0
Several species introduced all over the world
Mainly for food, also bait, aquarium trade
Most invasives from North America
In Europe 5 native, 16 non-native species
Worse invaders: signal and red swamp crayfish
IMPACTS: ◦ Carry crayfish plague
◦ Out-compete native species
◦ Degrade river habitats & ecosystems
Introduced to Britain in the 1970’s
Highly invasive, have spread throughout UK
Virile Crayfish Red Swamp Crayfish
Peay et al. 2009, KMAE
Predation of fish at high density signal crayfish, c.20-30 m-2
Based on the River Barle in Exmoor National Park
Signal crayfish have colonised 15km of the SSSI
Major risk to the SSSI, salmonids and the river’s Water Framework Directive status
The project is subject to PhD research by N. Green supported by Bournemouth
University, EA and CEFAS.
◦ Trapping – standard traps select dominant males
◦ Electrofishing – only suitable for small watercourses, possible fish damage, doesn’t catch all animals
◦ Dewatering – only suitable for small watercourses
◦ Biocides – too much risk to ecosystem
◦ Barriers – effective in certain localities
◦ Research always ongoing,
e.g. GM, poison
Conventional baited trapping tends to catch large adults. Large males control breeding behaviour so their sterilisation and return maintains dominance whilst preventing successful mating.
Lab studies indicate manual sterilisation of males may be effective at eradication (CEFAS & Newcastle University)
Initial results in France highly
successful, never been trialled
in rivers in the UK
Combined with intensive
trapping using two methods
1.5km trial stretch near Withypool
Intensive trapping using two types of trap over three years – weekly in 2015
Large male crayfish are neutered manually and returned, whilst all other animals are humanely despatched.
Success will be measured by monitoring invertebrates, fish, young-of-year and berried female crayfish between 2015 and 2018.
Baited traps Artificial refugia
3275 crayfish captured
2848 humanely killed
427 large males sterilised – 13% of total
Baited traps less efficient but good in autumn
Weather – flow levels are a major constraint
Baseline data on invertebrates, fish & juvenile crayfish collected
Data analysis will inform future works
Volunteers are key….
Partnership project
Financial and in kind support from ENPA, EA, NE and RETA
No funding for PhD research!
• Report sightings to EA • Practice biosecurity –
check, clean dry! • Fund my PhD!