I have never seen such high interest rates for bitcoins on Poloniex.com before.
Lately the rates are between 36.5% to 109.5%.
Probably it is related to the likelihood of a bitcoin hardfork. Poloniex has announced their position on the possible hardfork: https://poloniex.com/press-releases/2017.03.17-Hard-Fork/
"What if I have my Bitcoin on loan at the time of the fork?
If you have Bitcoin on loan at the time of the fork, you do not have it on balance and therefore you cannot receive corresponding Bitcoin Unlimited."