I believe so, though I'm no CPA. And as long as you're still invested in something, I don't think you have to pay any taxes at all. Only when you sell.
I've been studying that very question. From what I have found you can deduct the whole amount from a gain in the following year.
HOWEVER, If you just have a loss you can only take 3,000 dollars of that loss a year. You will eventually get to claim the whole loss but only 3,000 a year.