A few weeks ago we posted a news item written by Chris Arthur, a Lancaster University masters student who has worked hard over the summer months on the Trust’s suggestion to investigate how signal crayfish (Pacifastacus leniusculus) are spreading in the Don Catchment. Well Chris has now written up his report and is available to download on our website below. It’s fascinating stuff and contains information useful for those trying to understand how we can manage our catchments to protect them from this invasive crayfish. It tackles such questions as is the observed distribution of crayfish in the Don Catchment the result of a single or multiple introductions, are signal crayfish spreading quickly, and are barriers influencing their spread?

Interestingly Chris found that signal crayfish exist in multiple discrete populations in the Don Catchment, indicating that they most likely originated as separate introduction events. For several of these, signal crayfish are also present in high densities in ponds adjacent to the infested river stretches, suggesting that these are the probable sources of the river populations. We would guess that the pond populations are the result of human introductions, either deliberate or unwitting.

Encouragingly, the river populations are expanding more slowly than has been observed in other catchments, meaning that if this does not change, it will take a while before the catchment is totally colonised. One population is bounded on its upstream side by a weir, suggesting that impoundments such as weirs can slow the spread of signal crayfish.

‘The distribution of the American signal crayfish (Pacifasticus leniusculus) in the Don River Catchment, South Yorkshire, UK’ – masters project by  Lancaster University student Chris Arthur
Part 1
Part 2
Part 3 

Signals in Chris’ crayfish trap. Credit Chris Arthur.