Nine eggs for 16 hens? That's not bad at all! I'm only getting 2 for 7 hens right now. If this is their second year laying, that would explain the decrease you've experienced over the winter.
Are you sure that you don't have some animal stealing your eggs? One winter I noticed decreased egg production and increased feed and water consumption. In the spring, I found out why. My coop just sat on the ground, and it was FULL of rats under there! Rats will steal and eat your eggs. (I also...