This 22 September 2019 WWF video says about itself (translated from Dutch):
For the first time in the history of the oysters released in our North Sea, offspring has been found. Four “baby” oysters born in the North Sea were discovered earlier this month during a diving expedition by Stichting Duik de Noordzee Schoon. In addition to these offspring, the adult and “adolescent” specimens are also doing very well.
European flat oysters (Ostrea edulis) had being practically extinct for almost a century. This is an encouraging sign.