Give me a call a few days before you get here, or once you are down here in Lima.
I do not how appropriate, or save, it is to provide you with my email and phone number through the open forum...send me an email and I will provide both for you so we can get in touch. Does this forum has a PM to contact each other privately?
December is right smack the begining of summer, so expect warmer conditions (5 mm is fine), water visibility is not that great so don't bring the heavy/long artillery.
Depending how long you will be staying down here, and your expectations, there are a multitude of spearfishing alternatives.