But is there any way to discover these areas without just gambling to find a fishing encounter along the shores for instance.
Not really. But BE SURE to read the text on the BACK of Terrain cards as you place them. First, they sometimes (rarely, but sometimes) contain important instructions which can break the game if they're not followed (been there, done that!). Secondly, they also often give you a hint that there are food sources available via one of the Actions printed on the card.