Habitat preference of different size classes of Austropotamobius pallipes in an Irish River

Abstract

Juvenile and immature crayfish are more difficult to find than adults and in consequence rather little is known about their habitat preferences. Smaller crayfish are able to inhabit different areas within the stream compared to adult crayfish. Whereas adult crayfish occur under stones and cobble in the river, juveniles and small individuals may be found along the margins, among rootlets and vegetation. A survey was carried at two sites in the Liffey catchment (Ireland) to assess habitat preference of crayfish according to size. A Surber sampler was used to collect crayfish in five types of habitat present at these sites. Each site presented a different distribution of crayfish amongst the habitat types. At Kilbride bridge, crayfish preferred cobble to pebbles and submerged and emergent macrophytes, while at Carragh bridge, crayfish were more dispersed throughout the habitat types. At both sites, juveniles and one year old crayfish were found in a variety of habitat types, whereas adults were only found in cobble and pebbles. The discrepancy in crayfish densities between the two sites can probably be explained by characteristics, such as depth and flow rate, that were not taken into account in the categorisation of the habitats.