A more thorough explanation:

FISH ROYAL

Fish royal refers to whales, sturgeon, and porpoises that are caught near the English coast or thrown ashore. These fish become the property of the Crown.

If a whale is found dead on the beach, it becomes fish royal and belongs to the Crown. Similarly, if a sturgeon is caught by a fisherman near the English coast, it also becomes fish royal.

Another example would be if a porpoise is caught in a fishing net, it would become fish royal and the Crown would have ownership over it.

These examples illustrate how fish royal works. Any fish that is caught or found near the English coast becomes the property of the Crown. This law was put in place to prevent people from profiting off of these valuable fish without the Crown's permission.