Recreational clam picking, called shiohigari in Japanese, is a traditional marine recreational activity which is still enjoyed by people today in Japan. For several decades, fisheries cooperatives have managed clam-picking parks appropriately to make sure that visitors to the parks can take enough clams back home and that clams in the parks are safe to eat, in other words, that shellfish toxin detected in the clams are within regulation limits. However, due to the decrease in the wild clam population in coastal areas in Japan and the more frequent detection of shellfish toxins in excess of the regulation limits, sustaining recreational clam picking in Japan has been hanging in the balance. Through interviews with managers of the clam-picking parks in Osaka and textual analysis of newspaper articles on shiohigari and shellfish toxin, the author found that the system of exchanging clams taken from the parks for those with shellfish toxin test safety certificates prepared by managers is socially accepted in Osaka. An online survey of 814 residents in Japan showed that appreciation of marine recreational activities such as shiohigari was the most influential among various marine ecosystem services in driving attitudes towards marine conservation. This suggests that efforts by clam-picking park managers, mainly fisheries cooperatives, not only provide valuable recreational clam-picking opportunities for people but also promote positive attitudes to marine conservation.