The prawns that are processed at the seafood buyers can be tubbed. They are not under the requirements and regulations that the harvesters are. In fact, they could be selling them in the same tubs that the harvesters are selling them in now.
Yes, you're making an important point. What will replace the locally caught harvest of prawns here if it's not available to the public is most likely going to be an inferior product from overseas, as many people find at the pubs and in the restaurants.