Trout & Salmon (UK) - - Letters -

What’s the prob­lem? In­va­sive crayfish are one of the great­est threats to fresh­wa­ter ecosys­tems world­wide. They were in­tro­duced to English fish farms in 1975, spread­ing widely, and were first recorded in Scot­land in 1995. In the UK, sig­nal crayfish are driv­ing na­tive white­clawed crayfish into ex­tinc­tion – if not by trans­mit­ting crayfish plague, which is lethal to white-clawed crayfish, then by out-com­pet­ing them with their larger size and faster growth. Sig­nal crayfish also dev­as­tate the wider en­vi­ron­ment, re­duc­ing over­all in­ver­te­brate biomass in in­fested wa­ters by more than 40 per cent. By un­der­min­ing banks with half-moon-shaped tun­nels up to 2m long, they in­crease ero­sion and dump silt into grav­els, which in­hibits suc­cess­ful spawn­ing by na­tive fish. Re­search by the Rib­ble Rivers Trust shows that they drive trout and other fish out of streambed refuges into ar­eas where they’re more vul­ner­a­ble to pre­da­tion. Sig­nal crayfish may also be re­spon­si­ble for the de­cline of many am­phib­ians.

What you can do

Take care­ful biose­cu­rity mea­sures when you leave an area where sig­nal crayfish are known or sus­pected to be present. Apart from strin­gent biose­cu­rity, no ef­fec­tive means of con­trol are cur­rently known. NB: Trap­ping sig­nal crayfish usu­ally re­quires a li­cence. If you catch an alien crayfish, it’s il­le­gal to re­lease it or al­low it to es­cape: crush­ing is usu­ally the most hu­mane means of dispatch.

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