Do nomads in Banished wait

You can trade for other types of livestock once you get a trading post up and running and a merchant arrives who has them to trade.

Crop fields will, on occasion, pull nearby workers to help harvest their yield. This is because designated farmers will turn the crop into food baskets and, on occasion, leave them to go do something else (bring food/firewood back their house, go to sleep, etc.) At this point, the food basket becomes a resource just laying around and any nearby citizen will pick it up and take it to the relevant storage facility. Said resource will now count as being produced by the citizen's work facility, leading to your fishing docks producing corn and (in my case) mines producing wheat.