Conserving the White-Clawed Crayfish in Hampshire

Southern Chalkstreams Project

Hampshire & Isle of Wight Wildlife Trust is a key partner of Vitacress Conservation Trust, working to safeguard our special chalk rivers and their threatened wildlife for over 25 years. Through the Southern Chalkstreams Project, the Trust is the lead organisation working in Hampshire to conserve the endangered white-clawed crayfish.

Running since 2016, the Southern Chalkstreams project is a partnership project between Hampshire & Isle of Wight Wildlife Trust and the Vitacress Conservation Trust, Environment Agency, Natural England and Bristol Zoological Society (BZS).

The White-Clawed Crayfish

The white-clawed crayfish Austropotamobius pallipes is the only species of crayfish native to the UK. Over 600 crayfish species have been identified globally.

This crayfish was once widespread throughout much of England and abundant within the chalk rivers of Hampshire, whose mineral-rich waters provide an abundance of calcium critical for the development of their hard exoskeleton. However, this species has been in decline since the middle of the 20th century, initially through localised extinctions due to inappropriate river management (e.g. dredging), pollution and over-abstraction. However, the rate of this decline dramatically accelerated from the mid 1970s, due to the introduction of the non-native invasive signal crayfish Pacifastacus leniusculus from North America.

The signal crayfish is larger, more aggressive, produces more eggs, and will both directly predate on and outcompete our native white-clawed crayfish. Furthermore this, and other invasive non-native crayfish species from North America, carry a disease – ‘crayfish plague’ – that they are effectively immune to, but that will cause mass mortality if introduced to a waterbody supporting white-clawed crayfish. This disease is the primary cause for the dramatic and widespread loss of our native species both nationally and in Hampshire. Its impact is amplified by the fact it can be spread without a crayfish host, transferred between waterbodies on muddy waders, fishing nets and other clothing and equipment.

The white-clawed crayfish, once widespread in rivers throughout our county, has suffered one of its most dramatic declines in Hampshire. Its current known distribution is focused on the three upper tributaries of the River Itchen Site of Special Scientific Interest (SSSI) / Special Area of Conservation: the Candover Stream, River Alre and Cheriton Stream. However, a small, highly isolated relic population was recently (re)discovered on a tributary of the River Test SSSI, and in January 2022 this species was re-discovered on the River Itchen near Winchester, at Winnall Moors Nature Reserve (owned by Hampshire & Isle of Wight Wildlife Trust).

White-clawed crayfish populations in Hampshire are isolated and highly vulnerable to loss, and without concerted effort it was feared this species would be completely lost from the county. In response to this real concern, the Southern Chalkstreams project was established in 2008 to deliver an ambitious programme of measures to ensure the long-term survival of this species in Hampshire.

Crayfish Project

The Southern Chalkstreams project is currently delivering a number of measures to protect, preserve and promote the expansion of white-clawed crayfish in Hampshire.

This includes:

  • Raising awareness of the issues threatening white-clawed crayfish (specifically non-native crayfish species and the deadly crayfish plague)
  • Delivering a well-established monitoring programme of existing white-clawed crayfish sites / maintaining an up to date knowledge of the distribution of non-native crayfish in Hampshire
  • Providing technical advice and guidance to partner organisations, stakeholder groups and relevant land / riparian owners to sympathetically manage and  enhance existing sites for white-clawed crayfish.

Further to this, the Trust has been working with the BZS on an exciting project to rear and breed white-clawed crayfish from Hampshire in captivity, for release both at new locations in the upper Itchen catchment, and at newly established ‘ark’ sites.

Project Successes and Highlights

Here are some of the main successes and highlights of the project since its inception:

  • Established a captive-rearing and breeding programme led by the Bristol Zoological Society, with over 3,500 white-clawed crayfish of River Itchen provenance born in captivity since 2013.
  • Over 1,400 of these individuals have been released into the Candover Stream since 2014 to extend the upstream limit of white-clawed crayfish on this river, increasing its resilience to the potential future impacts of a pollution event or even climate change.
  • Through the strong relationships developed with landowners and partners, the project was able to confirm the rediscovery of white-clawed crayfish on the River Anton and at Winnall Moors Nature Reserve near Winchester, as well as the presence of a previously unknown sub-population of the River Itchen on the Cheriton Stream.
  • The project has influenced any future operation of a flow augmentation scheme on the Candover Stream, ensuring that the resident population of white-clawed crayfish were safe-guarded.

Project Updates

  • Our most recent release on the Candover Stream was aired on the 2022 edition of the BBC’s Autumnwatch.
  • This summer, the Ecology Team at the Hampshire & Isle Wight Wildlife Trust followed up their January (re)discovery at Winnall Moors Nature Reserve with a targeted survey programme at the site, recording over 70 crayfish on three different channels.
  • Footage of the berried female collection last spring, shown at the Hampshire and Isle of Wight Wildlife Trust’s 2023 AGM – Our white-clawed crayfish work.

    Current Work

    The project is currently focusing on:

    • Raising awareness of the plight of white-clawed crayfish and the importance of stringent biosecurity (see Golden Rules).
    • Working with land owners to establish white-clawed crayfish ark sites – these are isolated, self-contained new sites for white-clawed crayfish, populated with our captive-born individuals. They support permanent running and / or still water, and can support a healthy, self-sustaining population of white-clawed crayfish with little need for ongoing management.
    • In discussion with a potential new partner on the Isle of Wight to set up a small holding facility there.
    Crayfish and River Users

    Report Your Sighting

    If you have seen a White-Clawed Crayfish in the Hampshire area, let us know!

    Please email Dr Ben Rushbrook at with the sighting date, grid reference, suspected species and if possible, a photo.

    How Can I Help?

    Hampshire & Isle of Wight Wildlife Trust have put together these Golden Rules explaining how you can do your bit.

    Spores of the crayfish plague can remain active for around 6-22 days without a host and are lethal to native crayfish.

    Disinfect and dry
    Wet equipment and mud will harbour spores, so ensure boots / waders and equipment are thoroughly cleaned, disinfected and where possible allowed to dry.

    Plan visits
    Be aware of the distribution of crayfish and plan any visits (such as surveys) to minimise the risk of spreading plague. If possible, visit native sites first and signal sites afterwards.

    Work downstream
    If possible work in a downstream direction, rather than risk infecting upstream native sites with spores.

    Donor site
    If undertaking fish stocking or habitat enhancement works (such as planting
    marginal vegetation), consider the donor site carefully as fish and plant material can harbour plague spores. Plants may even conceal young crayfish.

    For more information, view the full Crayfish and River Users Guide here. 

    Our Other Projects…

    Riverfly Monitoring Initiative

    Riverfly Monitoring Initiative

    The Riverfly Partnership runs an invertebrate monitoring scheme which is of keen interest to anglers and wildlife enthusiasts alike who share a concern for the present and future health of our rivers. The initiative is based on the counting at regular intervals of key river insect species and other invertebrate groups as a method of assessing river quality.

    Tree Sparrow

    Tree Sparrow Project

    The Tree Sparrow is synonymous with mixed farming landscapes and was once widespread across Wiltshire and Hampshire, but are all but lost as a breeding species in the latter. Changes to agriculture and the loss of nesting sites have driven the population’s decline, although significant efforts have been exerted in Wiltshire to help their recovery.