Historical descriptions of Atlantic, Mediterranean, and Caribbean naval wars mention that merchant vessels of hostile nations would be routinely seized, sometimes openly and sometimes through privateers. Britain in particular achieved something like naval supremacy during the Napoleonic Era, able to intercept most Continental shipping of enemy states.
But what happened to fishing boats? Would they be captured as well? Would it be worth it to haul the boats back home to one's own fishermen? Or would they hide while enemy fleets were around? Would this cause a massive disruption to the food supply of certain countries?
Fishing boats were exempted from being taken as prizes during a naval blockade by customary international law. This was emphasised in the case Paquete Habana; the Lola, 175 U.S 677 (1900) where the court stated that:
By an ancient usage among civilized nations, beginning centuries ago and gradually ripening into a rule of international law, coast fishing vessels pursuing their vocation of catching and bringing in fresh fish have been recognized as exempt, with their cargoes and crews, from capture as prize of war.
In the judgement (page 175 U.S. 687), the court referred to orders issued by Henry IV in 1403 and 1406 called De Securitate pro Piscatoribus, made pursuant to a treaty entered into between England and France, which ensured that neither belligerent would capture the fishing vessels of the other's fishing fleet. A similar treaty is referenced as being entered into in 1521 between the HRE Charles V and Francis I of France.
I would love to be able to go into more detail as I've been meaning to do a deep-dive into the history and archaeology of naval blockades but it's being hampered by annoying things like full-time work.