Native white-clawed crayfish

The distribution of the white-clawed crayfish (Austropotamobius pallipes) is governed by geology and water quality. The species can be found in a variety of locations including canals, streams, rivers, lakes, reservoirs and water-filled quarries, where it occupies cryptic habitats.

Populations are concentrated in northern and central England.

They are largely nocturnal, with breeding taking place from September to November when water temperatures drop below 10°C for an extended period.

Habitat Preferences

• White-clawed crayfish occur in relatively hard, mineral-rich waters on calcareous and rapidly weathering rocks;
• Populations in the UK are associated with chalk, limestone or sandstone deposits in water bodies where calcium content is a minimum of 5 mg/l and pH ranges between 6.5-9.0 (alkaline); and
• Flowing water habitats in which the white-clawed crayfish is found often have undermined, overhanging banks; sections which exhibit heterogeneous flow patterns; cobbles and rock riffles; roots and woody vegetation; and under water-saturated logs.

• The white-clawed crayfish typically inhabits watercourses with depth ranging between 0.75-1.25 m. The species may also occur in very shallow streams (0.05 m depth) and in deeper, slow-flowing rivers (2.5 m depth);
• Populations occur in both still and running water. White-clawed crayfish can survive in rivers with a strong flow, providing suitable refuges such as weirs and boulders are present;
• They can occur in shallow riffles and in streams less than 0.5m wide with water depths of just a few centimetres;
• Low water levels can increase the white-clawed crayfish's vulnerability to predation;
• Flow conditions which affect bankside vegetation and submerged plant communities may have indirect consequences to white-clawed crayfish; and
• Increased silt loads (and turbidity) caused by land practices or flow changes (natural and induced) can clog the gills of crayfish. No quantitative data is available.

Other influences

• White clawed crayfish are susceptible to acute pollution incidents caused by spills of organic material with a high BOD (eg. cattle slurry).
• Oxygen levels below 5 mg/l for more than a few days in summer months may cause stress;
• Submerged plant communities and banks are required for refuge;
• The presence of overhanging bankside vegetation (for shelter, food and cover) may determine crayfish abundance;
• Direct predation and competition by the introduced signal crayfish (Pacifastacus leniusculus) has the potential to eliminate white-clawed crayfish populations. Signal crayfish may also act as vectors of the crayfish plague;
• Other non-native crayfish also have the potential to outcompete the white-clawed crayfish for resources; and
• Susceptibility to biocides is noted.