Signal crayfish (2020) – impacts upon fish and invertebrate communities

Strong impacts of signal crayfish invasion on upland stream fish and invertebrate communities


This study investigated the link between the invasive non-native signal crayfish (Pacifastacus leniusculus) and the abundance of native fish and invertebrates in a section of the River Tees. P. leniusculus are highly invasive due to their rapid growth, high reproductive capability and ability to thrive in a wide range of habitats. Three studies were carried out across 18 streams in 2011 and 2018;

      1. The assessment of fish and macroinvertebrates, these data were subsequently split into those streams invaded with P. leniusculus and those without.
      2. The second study, which was a subset of the first study, was to sample within-stream fish and macroinvertebrates in two Tees streams by comparing invaded and uninvaded sections over time.
      3. The third study analysed macroinvertebrates using historical data (1990-2018) and water quality data (1990-2018) in six of the 18 streams.

The combined figures enabled an evaluation of P. leniusculus on fish and macroinvertebrate communities in upland streams over time and distance scales. Linear mixed-effects modelling (LLM) was used to analyse fish densities, macroinvertebrate taxonomic richness and abundance data from uninvaded and invaded locations.

Over a seven year period, there were no significant changes between invaded and newly invaded streams, although the mean fish abundance decreased by 29% compared to a 93% increase in P. leniusculus across all streams.Negative effects from P. leniusculus on macroinvertebrates (reduced species abundance, and reduced larvae and immature stages) were recorded in invaded sections of streams, however higher abundance of macroinvertebrates (>125%) were recorded in uninvaded sites compared to invaded downstream sites. The results from this study highlights that both native fish abundance and the structure of fish and macroinvertebrates communities are strongly affected by P. leniusculus despite river habitats remaining the same.

Galib, S.M., Findlay, J.S. and Lucas, M.C. (2020). Strong impacts of signal crayfish invasion on upland stream fish and invertebrate communities. Freshwater Biology, 66(2), pp.223–240.


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Invasive Species Ireland

Invasive Species Ireland