I think that if the incoming management has determined that high turnover is impacting the restaurant's productivity in a negative manner, it must make the retention of employees as one of its top priorities. This can involve in assessing where the turnover reality lies.
If it is a lack of compensation, perhaps a new salary scale with better benefits and greater incentivizing packages can become more alluring to employees, thereby reducing the turnover evident. If the lack of employee voice and constant feel of devaluing is a part of the process, management can implement new initiatives that value employee voice and perhaps even appropriate some of the workers into management positions that can help to bolster confidence and a sense of voice in what is being done.
Another approach is to reach out in a distinct and individualized manner to the current employees, articulating to them that they, the workers, are going to be essential to the new transition. Using this as a motivational technique as a "new start" could be another way in which employee turnover is addressed and the process of retention is begun in an effective manner.
The reality is that if turnover is deemed as something that must be avoided, management has to invest time and resources either prior to entering or in its initial entrance to ensure that the issue of employee turnover is addressed. Involved in this is the institutional courage to examine and reexamine policies and practices, evaluating their overall impact on employee and management relationships in the issue of turnover and retention.