>>1880693https://en.service-public-particuliers.gouv.mc/Free-time/Sport-and-recreation/Permits-and-certificates/How-to-request-a-authorisation-for-underwater-fishingPage is directed towards underwater fishing but does state:
>Fishing of any kind is forbidden:>In harbours, and in the entrances to ports in Monaco>In maritime areas where work is being carried out and where public access if forbidden, as set out in ministerial decrees 