Tuesday November 28th, 2006
The story so far - aliens sneak in and start eating or replacing the locals. The aliens are ugly and/or sexually promiscuous or deviant. We want them gone! Sounds like a brief outline of a SciFi film?
Didymo in New Zealand.
Signal crayfish in the UK.
New Zealand mud snails in the US.
Gyrodactylus in Norway.
I doubt anyone knows for sure how these all these species crossed borders or jumped continents.
Signal crayfish arrived in the UK perfectly legally as a faster growing crop. Larger and more prolific than our native crayfish, when released into the wild they chomped their way through the locals. Somehow, signal crayfish have "jumped" from river to river, angling may be one way they make that jump.
New Zealand mud snails are endemic to New Zealand and have naturalized in Australia, Europe and the North America. Exactly how mud snails spread, ships ballast, with live fish or on recreational gear is unknown. Somehow, mud snails jumped from river to river, angling is one way they make that jump.
Imports of Baltic salmon introduced Gyrodactylus Salaris to Norway. Unlike Baltic fish Atlantic salmon have no immunity to the parasite. Again it spread, by man and fish. Again angling is one of the vectors.
Didymo (Didymosphenia geminate) aka rock snot is indigenous to the northern hemisphere. In pristine New Zealand waters, it is having a ball. Again, man was probably how Didymo hitched south of the equator, and is almost certainly how it spreads from river to lake. Again, angling is one of the vectors by which it spreads.
No matter where you fish CLEAN YOUR GEAR!
PS Btw invasive species are far from rare.