Dump every villager old enough into the ocean to fish and watch them closely, dragging any that walk out without a fish back in again to try again. Your food stocks should soon start to climb to a safe level again.

I can't offer much better advice on repopulation than keza's - get them kissing! Make sure as many women of child-bearing age as possible are set to parenting so they'll contiue to have babies while the game is closed.