Flat Oysters Reintroduce Themselves

European flat oysters have not been seen in Belfast Lough for over 100 years. Scientists were consequently surprised to find substantial numbers of these edible bivalves in the Lough, apparently without the aid of a reintroduction programme (https://www.theguardian.com/environment/2020/dec/26/oysters-return-belfast-lough). There have been reintroduction programmes for European flat oysters in a number of European locations, as the species has been threatened by the introduction of the alien Pacific oyster in fisheries. Perhaps all that was needed in Belfast, was an improvement in the nutrition content of the waters of the Lough and the spat followed?