The only other food source that comes to mind is from mushrooms that the kids collect. Constant monitoring of the village can make maximum use of this resource.
Food consumption is probably less than you would imagine, however. On the order of 20 food units per villager per village year (which depends on game speed selected), from what I have seen. So, you might have enough food to last till you can get enough tech points to by level 3 of farming. And, even if your food drops to nothing, it still takes a long time for the villagers to suffer enough starvation damage to die.
In future villages you might want to consider keep the population down so that the overfishing that causes the algae never takes place till about the time you can eliminated it with level 3 farming.
Jer
My cat is good for nothing, but he's very, very good at it.