Perhaps anyone listening to the plane announcements, looks at any one of the multitude of signs on arrival, or anyone (everyone) who fills out the incoming passenger card? It’s not at all unclear what you have to do when you’re there. They make it clear to declare everything at multiple points. There is no penalty for declaring something even if it’s not allowed in.

On the first side of the incoming passenger card, half of it is taken up by the question:

Are you bringing into Australia:

[…]

6. Meat, poultry, fish, seafood, eggs, dairy, fruit, vegetables?

7. Grains, seeds, bulbs, straw, nuts, plants, parts of plants, traditional medicines or herbs, wooden articles?

8. Animals, parts of animals, animal products including equipment, pet food, eggs, biologicals, specimens, birds, fish, insects, shells, bee products?