Where have all the tadpoles gone?

[lavenderlux]

'Where have all the tadpoles gone' is something we'd been asking about our allotment wildlife pond this year - we had masses of frogs and frogs spawn but no tadpoles.  We'd put it down to the cold Spring but today when a family was doing a pond dip one of our plot holders came by and said to be careful of the crayfish - and told us that he'd been there when another plot holder had put a bucketful of young American crayfish into our pond last Autumn.    I am absolutely horrified and to me this seems like an act of vandalism.  Pond dipping is an activity many of our plot holders with families like to do and something we do with our schools groups, although we hadn't done any this year because there's been nothing there - and this is probably why.   We also seem to be lacking damselflies and dragonflies this year - and having looked up American crayfish, it seems they eat almost anything in the way of pond life.   
Does anyone have any answers on how to get rid of them - its a man made pond with a liner about seven feet by ten feet, so perhaps if we drain it we'd be able to get them out and destroy them, but this would be quite a major task

[Unwashed]

That's increadibly frustrating.  I don't think there's any alternative but to drain it down.

[irnhed]

That's terrible. 

You'd have to drain it down, but there could be eggs anywhere, so you'd have to rinse down any vegetation, scoop out & replace any bottom mud etc.

Perhaps you can check what the American Crayfish breeding cycle is, to try and clear out when there shouldn't be any eggs around, that should help.

The American Crayfish are all over the place in British Waterways, and they're pushing out the native crayfish species, kinda like grey squirrels pushing out the reds (I'm sure you're already aware if you've looked into them).

If someone did do it deliberately, what a horrible person.  It was either very ignorant, or very, very malicious.

[lavenderlux]

Thanks for your replies;  told our field secretary this morning about the crayfish and he's of the opinion that this person should assist in the clearing of our pond.  It will have to be in September or October as we are extremely busy on the allotment at the moment - open day, field BBQ, visitors from other allotment groups, schools visits - and its going to make a mess.  One of our plot holders has a pump which we can use and we have a generator and we can probably pump the water out into ourHazel coppice
The person who did this said he didn't realise the damage they could cause, he's also put crayfish in an ornamental pond in the grounds of a property where the company he works for as a groundsman looks after the landscaped gardens - don't think they'd be very pleased if they find out