The Naval Service vessel LÉ Róisín (P51) has detained a Spanish registered fishing vessel approximately 95 nautical miles south of Mizen Head.
A spokesperson for the Defence Forces said that the detention was in relation to alleged breaches of fishing regulations.
The vessel will be escorted to port, where on arrival it will be handed over to An Garda Síochána.
This is the fifth vessel detained by the Naval Service in 2021.
The Defence Forces conducts at sea fishery inspections in line with the service level agreement with the Sea-Fisheries Protection Authority, as part of its delivery of government services to the state.