Differentiate Author and User Storage Service?

Quick design decision here. Do we want to have a single storage service interface that does both Author and User stuff, or do we want to do the following:

IUserService { GET stuff }

IAuthorService extends IUserService { PUBLISH stuff }

StoryManager implements IAuthorService;
LocalDb implements IAuthorService;
WebService implements IAuthorService;

This way all User activities always declare the storage as IUserService and Author activites declare the storage as IAuthorService, yet they are actually exact same item. Or there is actually two seperate implementations (author extending user again).

Which one should we go for?