The Sea-Fisheries Protection Authority (SFPA) has seized 194 lobsters from Ballyconneely in County Galway because they were below the minimum legal size.
The SFPA says it took action after a tip-off from a member of the public.
All lobsters were unshackled and returned to the sea, the SFPA said.
The Sea-Fisheries Protection Authority is responsible for upholding Irish and European law and ensuring compliance with the EU’s Common Fisheries Policy.
Bringing ashore lobster smaller than 87mm in length is illegal.
Fishermen and women are also not allowed to catch lobsters marked with a ‘v’ notch as these lobsters are protected for breeding, the agency added.
“The scale of such a find of undersize lobsters is concerning and signals a significant threat for the future viability of the fishery”, said Paschal Hayes from the SFPA.
“The fishery for lobster is one of the most traditional fisheries among coastal communities and the mainstay of many small vessels fishing all around the coast of Ireland.
The actions of a few fishermen selling undersize and v-notch lobsters undermine the legitimate fishermen trying to maintain a sustainable fishery and livelihood.”
It comes as the agency has been working over the summer to double down on EU fisheries rules.
The agency conducted 11 surveillance flights between July and August and 40 inspections.
The SFPA said it was particularly monitoring fishing activities within Ireland’s Exclusive Economic Zone (EEZ), an area stretching 200 nautical miles from the Irish coastline.
Part of the zone is considered a vulnerable marine ecosystems where certain types of bottom trawling fishing is prohibited.