New homes wanted for Hampshire crayfish

The Trust is seeking to secure the long-term survival of native white-clawed crayfish in Hampshire by finding or creating new ‘ark’ sites. These sites will allow these endangered crustaceans to live free from the threat of non-native species and other pressures, and we think you might be able to help!

Non-native signal crayfish are much larger than the native species.

The UK has just one native species of freshwater crayfish - the white-clawed crayfish. Our native species typically spends its days hidden away in crevices and under rocks, coming out at night to forage for food. White-clawed crayfish eat a range of freshwater food, from plant matter to carrion and small invertebrates. Sadly, their population has declined by over 90% in Hampshire since the 1970s. This decline has been driven by a combination of habitat loss, pollution, insensitive river management and, crucially, the introduction and spread of non-native crayfish species. One in particular, the North American signal crayfish, has become established and widespread in English waterways. Larger and more aggressive than their European relatives, signal crayfish have driven white-clawed crayfish out of much of their historic range. However, of even greater impact has been the fungal disease known as crayfish plague. Signal crayfish carry this disease and are largely immune to it themselves, but it will wipe out whiteclawed crayfish populations if the spores get into a water body where they are present. These spores can be carried by signal crayfish themselves or transferred on the boots, waders, wetsuits or fishing equipment of people visiting our rivers, streams, lakes and ponds.

A site on the Upper Itchen that currently supports white-clawed crayfish.

Boosting numbers

In Hampshire, white-clawed crayfish are now only found in the headwaters of the River Itchen and on a tributary of the River Test. With the support and collaboration of key partners, the Vitacress Conservation Trust, the Environment Agency, Natural England, Sparsholt College and the Bristol Zoological Society, the Trust’s Southern Chalkstreams Project has been working to expand the range of the River Itchen population. This has been achieved by collecting female crayfish with clutches of eggs and taking them into a specialist hatchery at Bristol Zoo Gardens.

A female white-clawed crayfish (with eggs).

After their eggs hatch, the females are returned to the wild, and their young are reared in the relative safety of captivity. Once the juveniles are large enough, they are released into suitable parts of the river, upstream of their known populations. Using this method, we have released more than 1,000 juvenile crayfish since 2014. Our ecology team continues to monitor their numbers to ensure the crayfish populations remain healthy and to check that no non-native species are present.

Creating arks

Now, we are looking to establish ‘ark’ sites for white-clawed crayfish. Named after the biblical Noah’s Ark, these are isolated, self-contained sites that will include river headwaters, lakes and ponds. They will be able to support healthy, self-sustaining populations of crayfish with little need for ongoing management.

To meet the criteria of an ark site the waterbody must be free of any existing crayfish populations and have little or no recreational activity, such as water sports, dog swimming or stocking with fish for angling. Also, they must not dry up during the summer and should be no smaller than 0.1 hectare (1000m 2 ) in size.

By far the most important criterion is the absence of and low risk of colonisation by non-native crayfish species. We are therefore aiming to position all our ark sites more than 2 kilometres away from anywhere a signal crayfish has been recorded. Finding suitable sites has proved difficult so far, due to the widespread distribution of signal crayfish in Hampshire.

After conducting a map-based study, we think that areas with most ark site potential are in the north of Hampshire, from the west of Andover across to Basingstoke, and in the east of the county, in the areas to the north and south of New Alresford.

Juvenile crayfish release in the Upper Itchen.

Over to you

Now we are turning to you, our members, for help. If you are an interested landowner whose land includes bodies of water with ark site potential, or if you think you may know of such a site, please contact the Trust on Ben.Rushbrook@hiwwt.org.uk.

Finally, there is something we can all do to stop the spread of crayfish plague and other invasive species, helping to protect white-clawed crayfish. Remember to ‘check, clean and dry’ before and after visiting our rivers, streams, lakes and ponds:

Check your clothes, footwear and fishing equipment for live organisms, leaving them at the water body where you found them.

Clean and wash mud and plant material off all equipment, footwear and clothing.

Dry all equipment and clothing - in direct sunlight if you can - as some micro-organisms can live for many days in damp conditions. Make sure you do not transfer water between sites.

www.nonnativespecies.org/ checkcleandry