Hi, Jim.
Having seen U-tube videos of dozens of large silver carp leaping into the air in panic at the approach of a small boat, it is easy to understand the concern.....and how the term “aggressive” came to be applied to an introduced species which feeds exclusively on plankton (or so I read on Wikkipedia and elsewhere).
http://www.telegraph.co.uk/news/worldnews/northamerica/usa/10646283/US-moves-to-curb-invasion-of-aggressive-Asian-carp.html The pressure to DO something becomes extreme!
That said, ill considered, poorly researched “quick fixes” such as the farcical Rotenone poisoning schemes (see link
http://www.counterpunch.org/2009/12/09/how-to-kill-a-carp/ ) have a long history of disastrous failure - and spending $18 billion to protect an already degraded ecosystem (with no guarantee of success) seems pointless. Perhaps your “leave it for a century” suggestion would be the less damaging option.
However, I don't think the same approach should be applied to all cases. Otherwise pristine ecosystems or areas where an entire rare species could be wiped out – such as Lake Bala, don't forget – need special, thoroughly researched treatment. If this requires a total ban on recreational use of such waters by visiting boats, so be it!
We have lived for at least two centuries in an era when wildlife (for want of a better expression) needs protection from humans, not the other way around.
Andy.
Your suggestion that we eat our way out of the plague of American Signal Crayfish sounds good (and they certainly taste good - and are twice the size of the native species I used to catch as a nipper!) but it ain't that simple:-
Large Signal crayfish can be cannibalistic, so in areas where they haven't yet bumped off all the native species, removing the big daddy Signals means a population explosion of smaller Signals, eating everything in sight to take over top spot. Unfortunately this includes the poor little natives. Ooops!
Crayfish trappers, canoeists and presumably, trailer sailors moving from water to water, are quite likely to spread spores of the fungal disease, crayfish plague, often carried by Signals, which native species have no resistance to. Incidentally, power washing your boat and trailer will not remove all the microscopic life they've picked up. The fungal spores can survive for at least two weeks on damp clothing, wet tyres etc. Strong Iodoform disinfectants will kill them, along with anything else it meets on its way down through the water table! Luckily, dunking everything in the sea will do it, too. (After you've infected every ditch you pass on the way to the sea, that is!)
Check out the link for more bad news!
http://www.environment-agency.gov.uk/homeandleisure/recreation/fishing/38045.aspx