Invasive crayfish

A Spotlight Specimens special for Oxford Festival of Nature

By Sancia van der Meij, Research Fellow

The White-Clawed Crayfish (Austropotamobius pallipes) is often assumed to be native in the UK, but was in fact brought across by monks in the Middle Ages from northern France

In the 1970s this was joined by a further seven invasive crayfish species from other parts of the world, but mainly from North America. Some of these species have a very restricted distribution in the UK, such as Procambarus acutus which is only known from a single pond in Windsor.

The most widespread of these is the Signal Crayfish, Pacifastacus leniusculus, which was introduced to Europe in the 1960s and reached the UK by 1975. It is now widespread in waterways around England, Wales and parts of Scotland. There are records of Signal Crayfish from all over Oxfordshire, in the River Thames, River Cherwell, canals and ponds, and they are fished for by many people as sport or food.

The Signal Crayfish is so named because of the blue-white patches on the underside of its claws, next to the finger joint. It is the easiest invasive species to identify given its large size, smooth carapace and signal spots.

There are a number of information sites to help with identification such as the UK Crayfish Hub run by Buglife. The Non-Native species website runs a recording scheme for sightings of all invasive species too. Don’t worry though, the huge Tasmanian Giant Crayfish (Astacopsis gouldi) shown in the video clip has not made it to our waterways!

Whilst increased levels of water pollution and habitat degradation, fragmentation and loss have played their part in the decline of many crayfish populations, several species are also significantly impacted by the introduction and spread of a disease known as ‘crayfish plague’, a fungal disease is carried by some  North American species.