White-clawed crayfish for the uninitiated Part 2

Thursday, November 29th, 2012

After we had disinfected ourselves and our equipment back at our vehicles we moved on to our second stop; part of the River Wensum which supports a colony of non-native signal crayfish (Pacifastacus leniusculus). The River Wensum is here wide and shallow, with a substrate of sand and stones, and low clay banks fringed by woodland.

Signal crayfish in the net – Photo  Alex Prendergast

It wasn’t long before Danny Thomas found the first signal crayfish, a small two year-old individual, but we hoped for much larger specimens!  Several modest-sized signals were caught until Wendy McFarlane found the day’s prize catch; an enormous (but dead) male, with claws 10cms long! Signal crayfish burrows riddle the bank here to the extent that sections collapse, providing views of the interior of some burrows. Understandably no-one wanted to see if anything was living in the holes using the standard method of finger poking so we resorted to sticks.

Once again we all disinfected and headed off to our third and final site on the bank of the River Yare below Norwich where Alex had previously recorded dead Turkish, or narrow-clawed crayfish (Astacus leptodactylus), and hoped to find some live animals. Here we checked refuge traps set a few nights earlier, but unfortunately nothing had moved in.

At the end of the day Alex invited all to the pub to discuss crayfish matters and study pickled specimens with crustacean colleagues. Surprisingly no-one accepted the offer and the rest of the group headed home only to be confronted by a tree blown onto the railway line by the day’s gales, which meant a long wait at Diss station; possibly still preferable to an evening with a jar of pickled crayfish.

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