How do they find what they need? chapter 12

I think they just know that they are severely depleted. August, the end of the summer, brings about scarcity; they run out of oranges and grapefruits, the yam crop is destroyed by armadillos, the fish stop biting, and they run out of salt. Everyone in Fort Repose has depleted their salt supplies, and everyone is suffering. The absence of fish is inexplicable and terrifying, as it is their main food source.