Abstract

Recruitment is a vital factor in the assessment, management and population dynamics of decapods. Since the juvenile stages of crayfish often prefer heterogeneous habitats, sampling with quantitative and reproducible methods have so far been challenging. We evaluate a new quantitative sampling method for juvenile crayfish; the enclosure trap. A field test was carried out during two consecutive years on a population of signal crayfish, Pacifastacus leniusculus, in littoral areas of Swedish Lake Erken. The densities of 0+ crayfish varied substantially with year, sampling date and substrate type. As expected, juvenile crayfish densities decreased over time in both study years, indicating a high mortality rate during their first year of life. Juveniles preferred gravel and stone over soft and sand substrates. Mean growth rate varied from 0.15 to 0.22 mm day^-1. We evaluate this method and present recommendations for how to design and optimize field studies using enclosure traps. We conclude that enclosure traps can be used to collect valuable data on density, growth and habitat preference of juvenile crayfish, thus providing useful information for studies on population dynamics and increasing the understanding of crayfish recruitment processes.

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